Fix WiFi show "Not connected" always issue

- The WiFi summary is designed to be changed when the
onCapabilitiesChanged() callback is made from the ConnectivityManager,
but there is no guarantee that there will be a callback after the
settings are registered to the ConnectivityManager.

- Need to fatch initial state information to show the correct summary
first when the settings register callback to the ConnectivityManager.

- Screenshot:
  https://screenshot.googleplex.com/AwmLX2ZQE2grC7N

Bug: 179335681
Test: manual test
- make RunSettingsRoboTests ROBOTEST_FILTER=WifiSummaryUpdaterTest

Change-Id: Ib5d22bdf34a3832dd5082e6e11cee699694afdee

tests/robotests/src/com/android/settings/wifi/WifiSummaryUpdaterTest.java

@@ -64,6 +64,14 @@ public class WifiSummaryUpdaterTest {
         verify(mWifiTracker).setListening(true);
     }
 
+    @Test
+    public void register_true_shouldFetchInitialStateAndSendSummaryChange() {
+        mSummaryUpdater.register(true);
+
+        verify(mWifiTracker).fetchInitialState();
+        verify(mListener).onSummaryChanged(anyString());
+    }
+
     @Test
     public void register_false_shouldUnregisterListenerAndTracker() {
         mSummaryUpdater.register(true);