Bluetooth: GATT: Handle ccc cfg values correctly on disconnect

 * clear non-bonded ccc cfg values as per BT spec
 * address compare logic
 * check if cfg_changed is defined

Change-Id: Id002f22a6aac1b918d743ef1e73b7e5c4768a229
Signed-off-by: Roger Lendenmann <roger.lendenmann@intel.com>