ifa_ifwithroute
struct ifaddr *ifa_ifwithroute(int, const struct sockaddr *,
ifa = ifa_ifwithroute(RTF_GATEWAY, gw, gw, fibnum);
info->rti_ifa = ifa_ifwithroute(flags, dst, gateway,
info->rti_ifa = ifa_ifwithroute(flags, sa, sa,
struct ifaddr *ifa = ifa_ifwithroute(flags, dst, &nh->gw_sa, fibnum);