Fix Firewalls panel to override the right method

Instead of overriding can_acess(), the panel check should
be overriding allowed() method instead. Overriding can_access()
will disable caching for the method.

Change-Id: Ibee85cdcf505e90d9faeb54dbab7216fc24c1b2c
Closes-Bug: #1403701
Merge "Fix Firewalls panel to override the right method"