ifnet_byindexgen
ifp = ifnet_byindexgen(m->m_pkthdr.rcvidx, m->m_pkthdr.rcvgen);
leaf_ifp = ifnet_byindexgen(m->m_pkthdr.leaf_rcvidx,
if_t ifnet_byindexgen(uint16_t idx, uint16_t gen);
if ((ifp = ifnet_byindexgen(mp->m_pkthdr.rcvidx,
ifp = ifnet_byindexgen(pkt->if_index, pkt->if_idxgen);
ifp = ifnet_byindexgen(pd.pf_mtag->if_index,