Show correct Wi-Fi status when switching to multi window mode

In WifiSettings, when switching to multi window mode,
WifiSettings fragment is recreated and "onPause()" is called,
then WifiTracker stops and wrong Wi-Fi status is shown.

Move "WifiTracker.startTracking()" to "onStart()",
 "WifiTracker.stopTracking()" to "onStop()"
to make sure to show correct Wi-Fi status.

Bug: 36078677
Test: Manual test OK

Change-Id: I215f180b1082f6039c03de8b4a3ca27d1f364c75

src/com/android/settings/wifi/WifiSettings.java

@@ -298,6 +298,8 @@ public class WifiSettings extends RestrictedSettingsFragment
 
         // On/off switch is hidden for Setup Wizard (returns null)
         mWifiEnabler = createWifiEnabler();
+
+        mWifiTracker.startTracking();
     }
 
     /**
@@ -317,7 +319,6 @@ public class WifiSettings extends RestrictedSettingsFragment
             mWifiEnabler.resume(activity);
         }
 
-        mWifiTracker.startTracking();
         activity.invalidateOptionsMenu();
     }
 
@@ -327,7 +328,11 @@ public class WifiSettings extends RestrictedSettingsFragment
         if (mWifiEnabler != null) {
             mWifiEnabler.pause();
         }
+    }
 
+    @Override
+    public void onStop() {
+        super.onStop();
         mWifiTracker.stopTracking();
     }