Fix the WifiTether test case failed

- Use the same service name(WifiManager.class) to mock
WifiManager.class

- Use the same service name(TetheringManager.class) to mock
TetheringManager.class

Bug: 184018452
Test: manual test
make RunSettingsRoboTests ROBOTEST_FILTER=WifiTether

Change-Id: I64741818d3455154866097f83e3a96c1c510e23b

src/com/android/settings/wifi/tether/WifiTetherBasePreferenceController.java

@@ -45,8 +45,8 @@ public abstract class WifiTetherBasePreferenceController extends AbstractPrefere
             OnTetherConfigUpdateListener listener) {
         super(context);
         mListener = listener;
-        mWifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
-        mTm = (TetheringManager) context.getSystemService(Context.TETHERING_SERVICE);
+        mWifiManager = context.getSystemService(WifiManager.class);
+        mTm = context.getSystemService(TetheringManager.class);
         mWifiRegexs = mTm.getTetherableWifiRegexs();
     }