in_control
ret = in_control(SIOCAIFADDR, (caddr_t)&ifra, ifp, NULL);
if (in_control(SIOCDIFADDR, (caddr_t)&ifr, ifp,
error = in_control(msg->control.nm_cmd, msg->control.nm_data,
int in_control (u_long, caddr_t, struct ifnet *, struct thread *);