RL_IP4CSUMTX_PADLEN
m->m_pkthdr.len < RL_IP4CSUMTX_PADLEN &&
(RL_IP4CSUMTX_PADLEN + 1 - m->m_pkthdr.len);
#define RL_RX_DMAMEM_SZ(sc) (RL_RX_LIST_SZ(sc) + RL_IP4CSUMTX_PADLEN)