ath_tx_findrix
ath_tx_findrix(rt, ic->ic_mcast_rate);
sc->sc_protrix = ath_tx_findrix(rt, 2*2);
sc->sc_protrix = ath_tx_findrix(rt, 2*1);
sc->sc_mcastrix = ath_tx_findrix(rt, sc->sc_ic.ic_mcast_rate);