Bluetooth: L2CAP: Fix not cleanup properly if ACL is disconnected

If ACL is disconnected with channels still active the code should call
l2cap_chan_del to clean it up properly.

Change-Id: Iffa9345a9697ac80c1f2295578c7161ffeb44420
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>