Bluetooth: Store address information in L2CAP channel structure

With the effort of abstracting the L2CAP socket from the underlying
L2CAP channel it is important to store the source and destination
address information directly in the L2CAP channel structure.

Direct access to the HCI connection address information is not
possible since they might not be avaiable at L2CAP channel
creation time. The address information will be updated when
the underlying BR/EDR or LE connection status changes.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>