Fix ApnSettings crash issue.

Steps:
1. Add a new APN;
2. Click 'Reset to default';
3. During reset, click the new APN;
4. Crash happened.
Solution:
Disable menu items when reseting default APN.

Bug: 28314239
Change-Id: I8df439d066e58039e9f91a9be642127eb7298159
1 file changed