Bluetooth: Remove l2cap_conn->src and l2cap_conn->dst usage from L2CAP

The l2cap_conn->src and l2cap_conn->dst addresses are just a pointers
to hci_conn structure. Use hci_conn->hdev->bdaddr and hci_conn->dst
directly instead.

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