NSEC2USEC
tdiff = NSEC2USEC(tnow - tprev);
hrtime_t delta = NSEC2USEC(now - zs->zs_start_time);
tcei->ce_rtt_sa = NSEC2USEC(tcp->tcp_rtt_sa >> 3);
tcei->ce_rtt_sum = NSEC2USEC(tcp->tcp_rtt_sum);