[Settings] Update UI when bluetooth connection is down.

- When Airplane mode on, all connection shall be disconnected. In
   current design, when bluebooth disconnected, network page in Settings
   does not udpate the UI.

Bug: b/246925011
Test: Maunal
Change-Id: I1bf56e96737157d8e76057028b22e94e0e8d76e4

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

@@ -72,6 +72,7 @@ public class TetherPreferenceController extends AbstractPreferenceController imp
 
                 public void onServiceDisconnected(int profile) {
                     mBluetoothPan.set(null);
+                    updateSummary();
                 }
             };