[EVPN-MH] Add CLI commands for EVPN VXLAN Multihoming configuration (#380)

#### Why I did it

This PR adds CLI commands to configure and monitor EVPN VXLAN Multihoming (EVPN-MH) feature in SONiC. These commands enable network operators to:
- Configure global EVPN-MH parameters (startup delay, MAC/neighbor hold times)
- Configure EVPN Ethernet Segments on LAG/PortChannel interfaces
- Set Designated Forwarder (DF) preference for load distribution
- Display EVPN ES, ES-EVI, and L2 nexthop information

This complements the EVPN-MH infrastructure added in sonic-swss and sonic-swss-common.

##### Work item tracking
- Microsoft ADO **(number only)**:

#### How I did it

**Global EVPN-MH Configuration** (evpn_mh.py):
1. **`config evpn-mh startup-delay <0-3600>`** - Configure EVPN-MH startup delay (default: 300s)
 - Determines how long to wait before declaring local Ethernet Segments as up after system boot
 - Prevents premature traffic forwarding during initialization
 - Valid range: 0-3600 seconds

2. **`config evpn-mh mac-holdtime <0-86400>`** - Configure MAC hold time (default: 1080s)
 - Duration to retain remote MAC entries after EVPN route withdrawal
 - Allows for graceful handling of temporary connectivity issues
 - Valid range: 0-86400 seconds

3. **`config evpn-mh neigh-holdtime <0-86400>`** - Configure neighbor hold time (default: 1080s)
 - Duration to retain neighbor entries after EVPN route withdrawal
 - Valid range: 0-86400 seconds

**Interface-level EVPN-ES Configuration** (main.py):
4. **`config interface evpn-esi add <interface> <esi>`** - Add EVPN Ethernet Segment Identifier
 - Supports two ESI types:
 - **Type 0 (Manual)**: `00:XX:XX:XX:XX:XX:XX:XX:XX:XX` - Operator-configured 10-byte ESI
 - First byte must be 0x00 (Type 0)
 - Validates against reserved ESIs (all zeros, all FFs)
 - Prevents duplicate manual ESI across interfaces
 - **Type 3 (MAC-based)**: `auto-system-mac` - Auto-generated from system MAC
 - Uses port ID derived from interface name
 - Leverages `system_mac` from PORTCHANNEL table if configured
 - Integrates with FRR via vtysh commands
 - Stores configuration in CONFIG_DB `EVPN_ETHERNET_SEGMENT` table

5. **`config interface evpn-esi del <interface>`** - Remove EVPN Ethernet Segment configuration
 - Removes from CONFIG_DB
 - Cleans up FRR configuration (es-id, es-sys-mac, es-df-pref)

6. **`config interface evpn-df-pref <interface> <1-65535>`** - Set DF preference
 - Controls Designated Forwarder election priority (higher value = higher preference)
 - Default: 32767
 - Valid range: 1-65535
 - Updates both CONFIG_DB and FRR configuration

**Show Commands** (evpn.py):
7. **`show evpn`** - Display general EVPN information
8. **`show evpn es [<esi>]`** - Display Ethernet Segment information
 - Optional ESI parameter to show specific ES details
9. **`show evpn es-evi [<vni>]`** - Display Ethernet Segment per EVI information
 - Optional VNI parameter to filter by specific VLAN/VNI
10. **`show evpn es-evi detail`** - Show detailed ES-EVI information
11. **`show evpn l2-nh`** - Display L2 nexthop groups for EVPN all-active ES

All show commands leverage FRR's `show evpn` commands via `bgp_util.run_bgp_show_command()`.

**Testing** (210+ test cases):
- config_evpn_mh_test.py - Global EVPN-MH configuration tests
 - Startup delay validation (boundary values, valid/invalid inputs)
 - MAC holdtime validation
 - Neighbor holdtime validation

- config_int_evpn_test.py - Interface EVPN-ES configuration tests
 - Manual ESI configuration (Type 0)
 - MAC-based ESI configuration (Type 3)
 - ESI validation (reserved ESI rejection, format validation, duplicate detection)
 - DF preference configuration
 - Configuration add/delete operations
 - Error handling and edge cases

**Helper Functions**:
- `is_reserved_esi()` - Validates against reserved ESI values
- `parse_esi_input()` - Parses and validates ESI input (Type 0 vs Type 3)
- `port_id_from_if_name()` - Extracts numeric port ID from interface name
- `check_if_same_manual_esi_exists()` - Prevents duplicate manual ESI configuration
- `run_vtysh_command()` - Wraps vtysh execution for FRR integration

**Files Changed**:
- evpn_mh.py - New file (109 lines)
- main.py - Added 199 lines for interface EVPN commands
- evpn.py - New file (67 lines)
- main.py - Added 2 lines to register EVPN command group
- config_evpn_mh_test.py - New file (104 lines)
- config_int_evpn_test.py - New file (230 lines)

**Total**: +711 lines across 6 files

#### How to verify it

**Global EVPN-MH Configuration**:
```bash
# Configure global EVPN-MH parameters
config evpn-mh startup-delay 600
config evpn-mh mac-holdtime 2000
config evpn-mh neigh-holdtime 2000

# Verify in CONFIG_DB
redis-cli -n 4 HGETALL "EVPN_MH_GLOBAL|default"
```

**Interface EVPN-ES Configuration**:
```bash
# Configure Type 0 (manual) ESI on PortChannel
config interface evpn-esi add PortChannel1 00:01:02:03:04:05:06:07:08:09

# Configure Type 3 (MAC-based) ESI
config interface evpn-esi add PortChannel2 auto-system-mac

# Set DF preference
config interface evpn-df-pref PortChannel1 50000

# Verify in CONFIG_DB
redis-cli -n 4 HGETALL "EVPN_ETHERNET_SEGMENT|PortChannel1"

# Verify in FRR
vtysh -c "show running-config" | grep -A 5 "interface PortChannel1"

# Delete ESI
config interface evpn-esi del PortChannel1
```

**Show Commands**:
```bash
# Display EVPN information
show evpn
show evpn es
show evpn es 00:01:02:03:04:05:06:07:08:09
show evpn es-evi
show evpn es-evi 1000
show evpn es-evi detail
show evpn l2-nh
```

**Run Unit Tests**:
```bash
pytest tests/config_evpn_mh_test.py -v
pytest tests/config_int_evpn_test.py -v
```

#### Which release branch to backport (provide reason below if selected)

- [ ] 202305
- [ ] 202311
- [ ] 202405
- [ ] 202411
- [ ] 202505
- [ ] 202511

#### Tested branch (Please provide the tested image version)

- [ ] <!-- image version 1 -->
- [ ] <!-- image version 2 -->

#### Description for the changelog

Add CLI commands for EVPN VXLAN Multihoming: global EVPN-MH configuration, interface Ethernet Segment (ESI) configuration, DF preference settings, and EVPN show commands

#### Link to config_db schema for YANG model changes

Updates required for:
- New table: `EVPN_MH_GLOBAL` - Global EVPN-MH configuration
 - `startup_delay`: 0-3600 (default: 300)
 - `mac_holdtime`: 0-86400 (default: 1080)
 - `neigh_holdtime`: 0-86400 (default: 1080)

- New table: `EVPN_ETHERNET_SEGMENT` - Per-interface ES configuration
 - `esi`: 10-byte ESI string (e.g., "00:01:02:03:04:05:06:07:08:09") or "AUTO"
 - `type`: "TYPE_0_OPERATOR_CONFIGURED" or "TYPE_3_MAC_BASED"
 - `df_pref`: 1-65535 (default: 32767)

YANG model updates should be submitted to sonic-yang-models repository.

#### Depends on

- sonic-swss-common PR: [Add L2 nexthop group table and raw netlink message handling support]
- sonic-swss PR: [EVPN-MH infrastructure and orchestration agents]
- FRR: EVPN MH support (available in FRR 8.x+)

---

**Key Features**:
✅ Global EVPN-MH parameter configuration
✅ Type 0 (manual) and Type 3 (MAC-based) ESI support
✅ DF preference configuration for load balancing
✅ FRR integration via vtysh
✅ CONFIG_DB persistence
✅ Comprehensive validation and error handling
✅ 210+ unit test cases
✅ Show commands for monitoring EVPN state

Signed-off-by: Sonic Build Admin <sonicbld@microsoft.com>

Author: mssonicbld

config/evpn_mh.py

@@ -0,0 +1,133 @@
+import click
+import utilities_common.cli as clicommon
+
+from jsonpatch import JsonPatchConflict
+
+from .validated_config_db_connector import ValidatedConfigDBConnector
+
+#
+# EVPN MH commands
+#
+EVPN_MH_TABLE = 'EVPN_MH_GLOBAL'
+
+#
+# 'evpn-mh' group ('config evpn-mh ...')
+#
+
+
+@click.group(cls=clicommon.AbbreviationGroup, name='evpn-mh')
+@click.pass_context
+def evpn_mh(ctx):
+    """Set EVPN MH attributes"""
+    pass
+
+
+#
+# 'startup-delay' subcommand
+#
+EVPN_MH_STARTUP_DELAY_MIN = 0
+EVPN_MH_STARTUP_DELAY_DEFAULT = 300
+EVPN_MH_STARTUP_DELAY_MAX = 3600
+
+
+def is_valid_startup_delay(startup_delay):
+    try:
+        if int(startup_delay) in range(EVPN_MH_STARTUP_DELAY_MIN, EVPN_MH_STARTUP_DELAY_MAX + 1):
+            return True
+    except (ValueError, TypeError):
+        pass
+    return False
+
+
+@evpn_mh.command('startup-delay')
+@click.argument('startup_delay', metavar='<startup_delay>', required=True)
+@clicommon.pass_db
+@click.pass_context
+def set_startup_delay(ctx, db, startup_delay=EVPN_MH_STARTUP_DELAY_DEFAULT):
+    """Set EVPN MH startup delay time in seconds"""
+    config_db = ValidatedConfigDBConnector(db.cfgdb)
+    if not is_valid_startup_delay(startup_delay):
+        ctx.fail(f"EVPN MH Startup Delay {startup_delay} is not valid. "
+                 f"Valid values are {EVPN_MH_STARTUP_DELAY_MIN}-{EVPN_MH_STARTUP_DELAY_MAX}.")
+
+    try:
+        # Get existing entry to preserve other fields
+        entry = config_db.get_entry(EVPN_MH_TABLE, 'default') or {}
+        entry['startup_delay'] = startup_delay
+        config_db.set_entry(EVPN_MH_TABLE, 'default', entry)
+    except (ValueError, JsonPatchConflict) as e:
+        ctx.fail("Failed to save to ConfigDB. Error: {}".format(e))
+
+
+#
+# 'mac-holdtime' subcommand
+#
+EVPN_MH_MAC_HOLDTIME_MIN = 0
+EVPN_MH_MAC_HOLDTIME_DEFAULT = 1080
+EVPN_MH_MAC_HOLDTIME_MAX = 86400
+
+
+def is_valid_mac_holdtime(mac_holdtime):
+    try:
+        if int(mac_holdtime) in range(EVPN_MH_MAC_HOLDTIME_MIN, EVPN_MH_MAC_HOLDTIME_MAX + 1):
+            return True
+    except (ValueError, TypeError):
+        pass
+    return False
+
+
+@evpn_mh.command('mac-holdtime')
+@click.argument('mac_holdtime', metavar='<mac_holdtime>', required=True)
+@clicommon.pass_db
+@click.pass_context
+def set_mac_holdtime(ctx, db, mac_holdtime=EVPN_MH_MAC_HOLDTIME_DEFAULT):
+    """Set EVPN MH MAC holdtime in seconds"""
+    config_db = ValidatedConfigDBConnector(db.cfgdb)
+    if not is_valid_mac_holdtime(mac_holdtime):
+        ctx.fail(f"EVPN MH MAC Holdtime {mac_holdtime} is not valid. "
+                 f"Valid values are {EVPN_MH_MAC_HOLDTIME_MIN}-{EVPN_MH_MAC_HOLDTIME_MAX}.")
+
+    try:
+        # Get existing entry to preserve other fields
+        entry = config_db.get_entry(EVPN_MH_TABLE, 'default') or {}
+        entry['mac_holdtime'] = mac_holdtime
+        config_db.set_entry(EVPN_MH_TABLE, 'default', entry)
+    except (ValueError, JsonPatchConflict) as e:
+        ctx.fail("Failed to save to ConfigDB. Error: {}".format(e))
+
+
+#
+# 'neigh_holdtime' subcommand
+#
+EVPN_MH_NEIGH_HOLDTIME_MIN = 0
+EVPN_MH_NEIGH_HOLDTIME_DEFAULT = 1080
+EVPN_MH_NEIGH_HOLDTIME_MAX = 86400
+
+
+def is_valid_neigh_holdtime(neigh_holdtime):
+    try:
+        if int(neigh_holdtime) in range(EVPN_MH_NEIGH_HOLDTIME_MIN, EVPN_MH_NEIGH_HOLDTIME_MAX + 1):
+            return True
+    except (ValueError, TypeError):
+        pass
+    return False
+
+
+@evpn_mh.command('neigh-holdtime')
+@click.argument('neigh_holdtime', metavar='<neigh_holdtime>', required=True)
+@clicommon.pass_db
+@click.pass_context
+def set_neigh_holdtime(ctx, db, neigh_holdtime=EVPN_MH_NEIGH_HOLDTIME_DEFAULT):
+    """Set EVPN MH neighbor holdtime in seconds"""
+    config_db = ValidatedConfigDBConnector(db.cfgdb)
+    if not is_valid_neigh_holdtime(neigh_holdtime):
+        ctx.fail(f"EVPN MH Neigh Holdtime {neigh_holdtime} is not valid. "
+                 f"Valid values are {EVPN_MH_NEIGH_HOLDTIME_MIN}-{EVPN_MH_NEIGH_HOLDTIME_MAX}.")
+
+    try:
+        # Get existing entry to preserve other fields
+        entry = config_db.get_entry(EVPN_MH_TABLE, 'default') or {}
+        entry['neigh_holdtime'] = neigh_holdtime
+        config_db.set_entry(EVPN_MH_TABLE, 'default', entry)
+    except (ValueError, JsonPatchConflict) as e:
+        ctx.fail("Failed to save to ConfigDB. Error: {}".format(e))