Refactor tether logic for reuse

Some logic related to permissions needs to be used elsewhere. This
CL refactors the relevant code into a method so that it stays in
sync in both places.

Test: robotests still pass
Bug: 64092292
Change-Id: I3b54529865e16b7e1640b0adda7f7edb9d1a41f7

src/com/android/settings/network/TetherPreferenceController.java

@@ -88,8 +88,7 @@ public class TetherPreferenceController extends AbstractPreferenceController imp
     public TetherPreferenceController(Context context, Lifecycle lifecycle) {
         super(context);
         mBluetoothPan = new AtomicReference<>();
-        mAdminDisallowedTetherConfig = checkIfRestrictionEnforced(
-                mContext, DISALLOW_CONFIG_TETHERING, UserHandle.myUserId()) != null;
+        mAdminDisallowedTetherConfig = isTetherConfigDisallowed(context);
         mConnectivityManager =
                 (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
         mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
@@ -170,6 +169,11 @@ public class TetherPreferenceController extends AbstractPreferenceController imp
         }
     }
 
+    public static boolean isTetherConfigDisallowed(Context context) {
+        return checkIfRestrictionEnforced(
+                context, DISALLOW_CONFIG_TETHERING, UserHandle.myUserId()) != null;
+    }
+
     @VisibleForTesting
     void updateSummary() {
         if (mPreference == null) {