Fix adding wifi configuration issue

- The Wi-Fi Enterprise Restrictions add a new
  UserManager.DISALLOW_ADD_WIFI_CONFIG restriction from T.

- When a user requests to add Wi-Fi configuration, Settings will
  reject the request if the user is not allowed.

- The above restriction need to be retrieved in advance so that the
  user's request will not be rejected.

- See the result screenshot in b/224459753#comment8

Bug: 224459753
Test: manual test
make RunSettingsRoboTests ROBOTEST_FILTER=AddAppNetworksActivity

Change-Id: I2dfb6b9946dd9dbd4eb8bf0f6549ac5cb4466f17

tests/robotests/src/com/android/settings/wifi/addappnetworks/AddAppNetworksActivityTest.java

@@ -39,15 +39,14 @@ public class AddAppNetworksActivityTest {
     @Mock
     private IActivityManager mIActivityManager;
 
-    private AddAppNetworksActivity mActivity;
+    private FakeAddAppNetworksActivity mActivity;
 
     @Before
     public void setUp() {
         MockitoAnnotations.initMocks(this);
 
-        mActivity = Robolectric.buildActivity(AddAppNetworksActivity.class).create().get();
+        mActivity = Robolectric.buildActivity(FakeAddAppNetworksActivity.class).create().get();
         mActivity.mActivityManager = mIActivityManager;
-        mActivity.mIsAddWifiConfigAllow = true;
     }
 
     @Test
@@ -92,4 +91,13 @@ public class AddAppNetworksActivityTest {
             // Do nothing.
         }
     }
+
+    private static class FakeAddAppNetworksActivity extends AddAppNetworksActivity {
+        boolean mIsAddWifiConfigAllow = true;
+
+        @Override
+        boolean isAddWifiConfigAllow() {
+            return mIsAddWifiConfigAllow;
+        }
+    }
 }