sdp(3): Change bdaddr parameter type in sdp_register_service()

Fixes compiler error when the caller passes a const bdaddr_t *
paramemeter (e.g., NG_HCI_BDADDR_ANY).

Sponsored by: The FreeBSD Foundation
MFC after: 1 day
Reviewed by: markj, emaste
Differential Revision: https://reviews.freebsd.org/D52582