Freeze netd AIDL interface (framework)

This freezes the interface as of the latest beta build, although it has
not changed since then.
This change adds the necessary implementations for getInterfaceVersion.

Test: flashed, WiFi working
Bug: 128803828
Change-Id: I43a6a38685d5fbc669cd573c4d7e7f99bd596952
diff --git a/services/core/java/com/android/server/NetworkManagementService.java b/services/core/java/com/android/server/NetworkManagementService.java
index 7875e93..1ff50b2 100644
--- a/services/core/java/com/android/server/NetworkManagementService.java
+++ b/services/core/java/com/android/server/NetworkManagementService.java
@@ -725,6 +725,11 @@
             ActivityManager.getService().notifyCleartextNetwork(uid,
                     HexDump.hexStringToByteArray(hex));
         }
+
+        @Override
+        public int getInterfaceVersion() {
+            return INetdUnsolicitedEventListener.VERSION;
+        }
     }
 
     //