[Settings] 1. Add configChange for WFC Activity to cover the changes of rotation and screen size

2. register split rule for MobileNetworkActivity

Bug: 204508876
Test: manual
Change-Id: Iff3dae41293e79b274d2928cb51efea46fb45dd4

src/com/android/settings/network/SubscriptionsPreferenceController.java

@@ -396,6 +396,8 @@ public class SubscriptionsPreferenceController extends AbstractPreferenceControl
     private static void startMobileNetworkActivity(Context context, int subId) {
         final Intent intent = new Intent(context, MobileNetworkActivity.class);
         intent.putExtra(Settings.EXTRA_SUB_ID, subId);
+        // MobileNetworkActivity is singleTask, set SplitPairRule to show in 2-pane.
+        MobileNetworkTwoPaneUtils.registerTwoPaneForMobileNetwork(context, intent, null);
         context.startActivity(intent);
     }