rum_txtime
dur = rum_txtime(pktlen, rate, ic->ic_flags) +
rum_txtime(RUM_ACK_SIZE, ackrate, ic->ic_flags) +
dur += rum_txtime(RUM_CTS_SIZE, rum_ack_rate(ic,
dur = rum_txtime(RUM_ACK_SIZE, rum_ack_rate(ic, rate),
uint16_t rum_txtime(int, int, uint32_t);