Freeze the networkstack-aidl-interfaces interface

This freezes the interface as of the latest beta build, not the tip of
tree. IIpClient#setL2KeyAndGroupHint is not in the frozen definition in
particular.

Generated with:
m networkstack-aidl-interfaces-freeze-api \
    ipmemorystore-aidl-interfaces-freeze-api

Test: flashed, booted, WiFi and captive portal working
Bug: 128803828
Change-Id: Ideabe73fc93bbefca2d624ee9ca190cf31419424

services/core/java/com/android/server/ConnectivityService.java

@@ -2817,6 +2817,11 @@ public class ConnectivityService extends IConnectivityManager.Stub
                     EVENT_PROVISIONING_NOTIFICATION, PROVISIONING_NOTIFICATION_HIDE,
                     mNai.network.netId));
         }
+
+        @Override
+        public int getInterfaceVersion() {
+            return this.VERSION;
+        }
     }
 
     private boolean networkRequiresValidation(NetworkAgentInfo nai) {