[AKS] Update network plugin defaults and long summary (#31516)

Signed-off-by: Sam Foo <samfoo@microsoft.com>

Author: sf-msft

src/azure-cli/azure/cli/command_modules/acs/_help.py

@@ -234,13 +234,13 @@
   - name: --network-plugin
     type: string
     short-summary: The Kubernetes network plugin to use.
-    long-summary: Specify "azure" for routable pod IPs from VNET, "kubenet" for non-routable pod IPs with an overlay network, or "none" for no networking configured. Defaults to "kubenet".
+    long-summary: Specify "azure" for highly scalable networking, "kubenet" for IP assignment from subnet NAT-based routing, or "none" for no networking configured. Defaults to "azure".
   - name: --network-plugin-mode
     type: string
     short-summary: The network plugin mode to use.
     long-summary: |
-        Used to control the mode the network plugin should operate in. For example, "overlay" used with
-        --network-plugin=azure will use an overlay network (non-VNET IPs) for pods in the cluster.
+        Used to control the mode the network plugin should operate in. Defaults to "overlay". If not specified with "azure" as
+        network plugin, pods are given routable IPs from VNET.
   - name: --network-policy
     type: string
     short-summary: Network Policy Engine to use.