BBR_INITIAL_RTO
t_rxtcur = BBR_INITIAL_RTO;
t_rxtcur = BBR_INITIAL_RTO;
f_rtt = BBR_INITIAL_RTO;
rexmt = USEC_2_TICKS(BBR_INITIAL_RTO) * tcp_backoff[tp->t_rxtshift];
srtt = (uint64_t)BBR_INITIAL_RTO;
tov = BBR_INITIAL_RTO;