tun_init turns interface/stack config into a set of flags that
tun(4) keeps in tun_softc sc_flags, but never uses. let's just cut
it out.

it keeps the current behaviour where setting an address implies
bringing the interface up though. i'm against this behaviour, but
it's harmless here.

ok?

Index: if_tun.c
===================================================================
RCS file: /cvs/src/sys/net/if_tun.c,v
diff -u -p -r1.241 if_tun.c
--- if_tun.c	10 Oct 2024 06:50:58 -0000	1.241
+++ if_tun.c	15 Oct 2024 03:30:27 -0000
@@ -123,7 +123,6 @@ int	tap_clone_create(struct if_clone *, 
 int	tun_create(struct if_clone *, int, int);
 int	tun_clone_destroy(struct ifnet *);
 void	tun_wakeup(struct tun_softc *);
-int	tun_init(struct tun_softc *);
 void	tun_start(struct ifnet *);
 int	filt_tunread(struct knote *, long);
 int	filt_tunwrite(struct knote *, long);
@@ -523,61 +522,6 @@ tun_dev_close(dev_t dev, struct proc *p)
 	return (error);
 }
 
-int
-tun_init(struct tun_softc *sc)
-{
-	struct ifnet	*ifp = &sc->sc_if;
-	struct ifaddr	*ifa;
-
-	TUNDEBUG(("%s: tun_init\n", ifp->if_xname));
-
-	ifp->if_flags |= IFF_UP | IFF_RUNNING;
-
-	sc->sc_flags &= ~(TUN_IASET|TUN_DSTADDR|TUN_BRDADDR);
-	TAILQ_FOREACH(ifa, &ifp->if_addrlist, ifa_list) {
-		if (ifa->ifa_addr->sa_family == AF_INET) {
-			struct sockaddr_in *sin;
-
-			sin = satosin(ifa->ifa_addr);
-			if (sin && sin->sin_addr.s_addr)
-				sc->sc_flags |= TUN_IASET;
-
-			if (ifp->if_flags & IFF_POINTOPOINT) {
-				sin = satosin(ifa->ifa_dstaddr);
-				if (sin && sin->sin_addr.s_addr)
-					sc->sc_flags |= TUN_DSTADDR;
-			} else
-				sc->sc_flags &= ~TUN_DSTADDR;
-
-			if (ifp->if_flags & IFF_BROADCAST) {
-				sin = satosin(ifa->ifa_broadaddr);
-				if (sin && sin->sin_addr.s_addr)
-					sc->sc_flags |= TUN_BRDADDR;
-			} else
-				sc->sc_flags &= ~TUN_BRDADDR;
-		}
-#ifdef INET6
-		if (ifa->ifa_addr->sa_family == AF_INET6) {
-			struct sockaddr_in6 *sin6;
-
-			sin6 = satosin6(ifa->ifa_addr);
-			if (!IN6_IS_ADDR_UNSPECIFIED(&sin6->sin6_addr))
-				sc->sc_flags |= TUN_IASET;
-
-			if (ifp->if_flags & IFF_POINTOPOINT) {
-				sin6 = satosin6(ifa->ifa_dstaddr);
-				if (sin6 &&
-				    !IN6_IS_ADDR_UNSPECIFIED(&sin6->sin6_addr))
-					sc->sc_flags |= TUN_DSTADDR;
-			} else
-				sc->sc_flags &= ~TUN_DSTADDR;
-		}
-#endif /* INET6 */
-	}
-
-	return (0);
-}
-
 /*
  * Process an ioctl request.
  */
@@ -590,8 +534,8 @@ tun_ioctl(struct ifnet *ifp, u_long cmd,
 
 	switch (cmd) {
 	case SIOCSIFADDR:
-		tun_init(sc);
-		break;
+		SET(ifp->if_flags, IFF_UP);
+		/* FALLTHROUGH */
 	case SIOCSIFFLAGS:
 		if (ISSET(ifp->if_flags, IFF_UP))
 			SET(ifp->if_flags, IFF_RUNNING);