Fix the consistency of connection status displayed on Wi-Fi card

- Refresh slice in WifiTracker.onConnectedChanged
- Only expose notifySliceChange to child in SliceBackgroundWorker

Fixes: 123270015
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.wifi.slice
Change-Id: Id5540ebae2746e58e14924665c5e62bf437ebcf0

tests/robotests/src/com/android/settings/wifi/slice/WifiSliceTest.java

@@ -139,4 +139,11 @@ public class WifiSliceTest {
 
         verify(mResolver).notifyChange(WIFI_SLICE_URI, null);
     }
+
+    @Test
+    public void onConnectedChanged_shouldNotifyChange() {
+        mWifiScanWorker.onConnectedChanged();
+
+        verify(mResolver).notifyChange(WIFI_SLICE_URI, null);
+    }
 }