systemui: Add CONNECTIVITY_INTERNAL permission

* SystemUI needs to be able to list interfaces if tethering is in use
   and we ask for a second tethering path to be set up (BT+USB, etc).
* Add permission to stop exceptions in the framework and enable
   tethering thru multiple paths.

Change-Id: I75b08a87f14c40b7f7c6a24d5bc4163ef86c3a01