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: If7a65c31557dc2f0451f0612fb109f61e8056368