TP_KEEPINTVL
tcp_timer_activate(tp, TT_2MSL, TP_KEEPINTVL(tp));
tcp_timer_activate(tp, TT_KEEP, TP_KEEPINTVL(tp));
#define TP_MAXIDLE(tp) (TP_KEEPCNT(tp) * TP_KEEPINTVL(tp))
ui = TP_KEEPINTVL(tp) / hz;