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

The l2cap_conn->src and l2cap_conn->dst addresses are just a pointer
to hci_conn->hdev->bdaddr and hci_conn->dst structures. Use the data
provided by hci_conn directly. This is done for hci_conn->dst_type
already anyway and with this change it makes it a lot clearer were
the address information comes from.

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