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

src/com/android/settings/wifi/addappnetworks/AddAppNetworksActivity.java

@@ -56,8 +56,6 @@ public class AddAppNetworksActivity extends FragmentActivity {
     final Bundle mBundle = new Bundle();
     @VisibleForTesting
     IActivityManager mActivityManager = ActivityManager.getService();
-    @VisibleForTesting
-    boolean mIsAddWifiConfigAllow;
 
     @Override
     protected void onCreate(@Nullable Bundle savedInstanceState) {
@@ -74,8 +72,6 @@ public class AddAppNetworksActivity extends FragmentActivity {
         window.setGravity(Gravity.BOTTOM);
         window.setLayout(WindowManager.LayoutParams.MATCH_PARENT,
                 WindowManager.LayoutParams.WRAP_CONTENT);
-
-        mIsAddWifiConfigAllow = WifiEnterpriseRestrictionUtils.isAddWifiConfigAllowed(this);
     }
 
     @Override
@@ -90,7 +86,7 @@ public class AddAppNetworksActivity extends FragmentActivity {
 
     @VisibleForTesting
     protected boolean showAddNetworksFragment() {
-        if (!mIsAddWifiConfigAllow) {
+        if (!isAddWifiConfigAllow()) {
             Log.d(TAG, "Not allowed by Enterprise Restriction");
             return false;
         }
@@ -129,4 +125,9 @@ public class AddAppNetworksActivity extends FragmentActivity {
         }
         return packageName;
     }
+
+    @VisibleForTesting
+    boolean isAddWifiConfigAllow() {
+        return WifiEnterpriseRestrictionUtils.isAddWifiConfigAllowed(this);
+    }
 }