EM_CSUM_FEATURES
ifp->if_hwassist |= EM_CSUM_FEATURES;
ifp->if_hwassist &= ~EM_CSUM_FEATURES;
} else if (m_head->m_pkthdr.csum_flags & EM_CSUM_FEATURES) {
ifp->if_hwassist |= EM_CSUM_FEATURES;
csum_flags = mp->m_pkthdr.csum_flags & EM_CSUM_FEATURES;