RL_CUR_TXMBUF
RL_CUR_TXMBUF(sc) = m;
while (RL_CUR_TXMBUF(sc) == NULL) {
BPF_MTAP(ifp, RL_CUR_TXMBUF(sc));
RL_CUR_TXMBUF(sc)->m_pkthdr.len);
if (RL_CUR_TXMBUF(sc) != NULL)