IFA_LIST_IFADDRHEAD
KASSERT((ifac->ifa_listmask & IFA_LIST_IFADDRHEAD) == 0,
ifac->ifa_listmask |= IFA_LIST_IFADDRHEAD;
KASSERT(ifac->ifa_listmask & IFA_LIST_IFADDRHEAD,
ifac->ifa_listmask &= ~IFA_LIST_IFADDRHEAD;