Add new no-op interface method.

Test: bit FrameworksNetTests:android.net.,com.android.server.net.
Test: bit FrameworksTelephonyTests:com.android.internal.telephony.dataconnection.DataConnectionTest
Change-Id: I46ab8fab705a6467f72b13b7dbc7f8af5f76fecf
Exempt-From-Owner-Approval: trivial no-op overload
Bug: 64133169

src/com/android/settings/datausage/DataSaverBackend.java

@@ -206,6 +206,10 @@ public class DataSaverBackend {
         public void onRestrictBackgroundChanged(final boolean isDataSaving) throws RemoteException {
             mHandler.post(() -> handleRestrictBackgroundChanged(isDataSaving));
         }
+
+        @Override
+        public void onSubscriptionOverride(int subId, int overrideMask, int overrideValue) {
+        }
     };
 
     public interface Listener {