tsig_update
tsig_update(&q->tsig, q->packet, buffer_position(q->packet));
tsig_update(&q->tsig, q->packet, buffer_limit(q->packet));
void tsig_update(tsig_record_type *tsig, buffer_type *packet, size_t length);
tsig_update(tsig, packet, buffer_position(packet));
tsig_update(&zone->latest_xfr->tsig, packet, buffer_limit(packet));