pfil_add_ihook
pfil_add_ihook(pfil_ifnet_wrapper, NULL, PFIL_IFNET, if_pfil);
pfil_add_ihook(pfil_ifaddr_wrapper, NULL, PFIL_IFADDR, if_pfil);
pfil_add_ihook(pppoe_ifattach_hook, NULL, PFIL_IFNET, if_pfil);
error = pfil_add_ihook(npf_ifhook, NULL,
error = pfil_add_ihook(npf_ifaddrhook, NULL,
int pfil_add_ihook(pfil_ifunc_t, void *, int, pfil_head_t *);