[Settings] Convert to getSystemService(Class<T>)

Change to getSystemService(Class<T>) to align the capability with framework
part.

Bug: 179640862
Test: local
Change-Id: I1b4812044fc4876bec6645570049a60f9470dbbd

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

@@ -255,7 +255,7 @@ public class TetherService extends Service {
     }
 
     private void disableTethering(final int tetheringType) {
-        final TetheringManager tm = (TetheringManager) getSystemService(Context.TETHERING_SERVICE);
+        final TetheringManager tm = getSystemService(TetheringManager.class);
         tm.stopTethering(tetheringType);
     }