Use BaseNetworkObserver in Tethering.

Tethering currently inherits from the AIDL interface
INetworkManagementEventObserver, so it has to provide no-op
implementations of all the interface's methods. Inherit from
BaseNetworkObserver and get rid of the no-ops.

[Cherry-pick of f4e90eac87]

Bug: 9180552
Change-Id: I74859b0d77951005651aaaa418185857e40eeedb

services/java/com/android/server/connectivity/Tethering.java

@@ -51,6 +51,7 @@ import com.android.internal.util.IState;
 import com.android.internal.util.State;
 import com.android.internal.util.StateMachine;
 import com.android.server.IoThread;
+import com.android.server.net.BaseNetworkObserver;
 import com.google.android.collect.Lists;
 
 import java.io.FileDescriptor;
@@ -70,7 +71,7 @@ import java.util.Set;
  *
  * TODO - look for parent classes and code sharing
  */
-public class Tethering extends INetworkManagementEventObserver.Stub {
+public class Tethering extends BaseNetworkObserver {
 
     private Context mContext;
     private final static String TAG = "Tethering";
@@ -315,14 +316,6 @@ public class Tethering extends INetworkManagementEventObserver.Stub {
         }
     }
 
-    public void addressUpdated(String address, String iface, int flags, int scope) {}
-
-    public void addressRemoved(String address, String iface, int flags, int scope) {}
-
-    public void limitReached(String limitName, String iface) {}
-
-    public void interfaceClassDataActivityChanged(String label, boolean active) {}
-
     public int tether(String iface) {
         if (DBG) Log.d(TAG, "Tethering " + iface);
         TetherInterfaceSM sm = null;