Bluetooth: Move bdaddr_to_le to hci_core

This patch moves the helper function bdaddr_to_le to hci_core, so it
can be used in mgmt.c and hci_conn.c.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Acked-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>