SNMP: narrow _cisco-metadata serial_number to entPhysicalSerialNum.1

The .67109120 index is only known on Catalyst 1300 / CBS-derived chassis;
those devices match the cisco-catalyst profile, which keeps its own
.67109120 lookup in _cisco-catalyst.yaml. Keeping .67109120 in the
generic Cisco mixin adds noise without coverage benefit.

Updates the changelog to reflect the narrower mixin scope.

Author: ian28223

snmp/changelog.d/23498.fixed

@@ -1 +1 @@
-Add ``entPhysicalSerialNum`` fallbacks for Cisco ``serial_number`` metadata. The Cisco Catalyst, Cisco Small Business (cisco-sb), and generic Cisco profiles now resolve ``serial_number`` from ``entPhysicalSerialNum`` at entPhysical indexes ``67109120`` (Catalyst 1300 / CBS350) and ``1``. Adds new Catalyst 9200 (``1.3.6.1.4.1.9.1.3079``) and Catalyst 1300 (``1.3.6.1.4.1.9.1.3233``, ``1.3.6.1.4.1.9.1.3236``) sysobjectids to the cisco-catalyst profile.
+Add ``entPhysicalSerialNum`` fallbacks for Cisco ``serial_number`` metadata. The Cisco Catalyst and Cisco Small Business (cisco-sb) profiles now resolve ``serial_number`` from ``entPhysicalSerialNum`` at entPhysical indexes ``67109120`` (Catalyst 1300 / CBS350) and ``1``; the generic Cisco profiles inherit ``entPhysicalSerialNum.1`` via the shared metadata mixin. Adds new Catalyst 9200 (``1.3.6.1.4.1.9.1.3079``) and Catalyst 1300 (``1.3.6.1.4.1.9.1.3233``, ``1.3.6.1.4.1.9.1.3236``) sysobjectids to the cisco-catalyst profile.

snmp/datadog_checks/snmp/data/default_profiles/_cisco-metadata.yaml

@@ -6,15 +6,13 @@ metadata:
       vendor:
         value: "cisco"
       serial_number:
-        symbols:
-          # ENTITY-MIB: entPhysicalSerialNum at entPhysicalIndex 67109120 — Catalyst 1300 / CBS-derived chassis.
-          # Reference: https://www.cisco.com/c/en/us/support/docs/smb/switches/Cisco-Business-Switching/kmgmt3636-snmpv3-common-oids-cbs350.html
-          - OID: 1.3.6.1.2.1.47.1.1.1.1.11.67109120
-            name: entPhysicalSerialNum
+        symbol:
           # ENTITY-MIB: entPhysicalSerialNum at entPhysicalIndex 1 — common chassis index.
           # Source: https://circitor.fr/Mibs/Html/ENTITY-MIB.php
-          - OID: 1.3.6.1.2.1.47.1.1.1.1.11.1
-            name: entPhysicalSerialNum
+          # Catalyst 1300 / CBS-derived chassis (which use entPhysicalIndex 67109120) match the
+          # cisco-catalyst profile, which provides its own serial_number lookup at that index.
+          OID: 1.3.6.1.2.1.47.1.1.1.1.11.1
+          name: entPhysicalSerialNum
       version:
         symbol:
           OID: 1.3.6.1.2.1.1.1.0