/*
* Depends on it isn't called in concurrent. It should be guaranteed
* by ifa->ifa_ifp's ioctl lock. The possible callers are in_control
* and if_purgeaddrs; the former is called iva ifa->ifa_ifp's ioctl
* and the latter is called via ifa->ifa_ifp's if_detach. The functions
* never be executed in concurrent.
*/