smb_compute_MAC
status = smb_compute_MAC(vcp, mp, rqp->sr_seqno, sigloc);
status = smb_compute_MAC(vcp, mp, rsn, sigbuf);
(void) smb_compute_MAC(vcp, mp, rsn + fudge, sigbuf);
(void) smb_compute_MAC(vcp, mp, rsn - fudge, sigbuf);