ALC_CSUM_FEATURES
if_sethwassist(ifp, ALC_CSUM_FEATURES | CSUM_TSO);
if_sethwassistbits(ifp, 0, ALC_CSUM_FEATURES);
if ((m->m_pkthdr.csum_flags & (ALC_CSUM_FEATURES | CSUM_TSO)) != 0) {
} else if ((m->m_pkthdr.csum_flags & ALC_CSUM_FEATURES) != 0) {
if_sethwassistbits(ifp, ALC_CSUM_FEATURES, 0);
if_sethwassistbits(ifp, 0, ALC_CSUM_FEATURES);