Added onRestrictBackgroundWhitelistChanged callback.

When users add or remove an app to the Data Saver Mode whitelist, the
app is notified through a
ConnectivityManager.ACTION_RESTRICT_BACKGROUND_CHANGED. But besides this
broadcast, it's also necessary to notify internal apps such Settings,
hence a new method is being added to INetworkPolicyListener.

BUG: 27481520
Change-Id: I1537a77becf6b7da1535ed5faabdc894fd9f7084

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

@@ -1419,6 +1419,15 @@ public class ConnectivityService extends IConnectivityManager.Stub
                 log("onRestrictBackgroundChanged(restrictBackground=" + restrictBackground + ")");
             }
         }
+
+        @Override
+        public void onRestrictBackgroundWhitelistChanged(int uid, boolean whitelisted) {
+            if (LOGD_RULES) {
+                // caller is NPMS, since we only register with them
+                log("onRestrictBackgroundWhitelistChanged(uid=" + uid + ", whitelisted="
+                        + whitelisted + ")");
+            }
+        }
     };
 
     /**