tun: set the flags before registering the netdevice

Otherwise, register_netdevice advertises the creation of the device with
the default flags, instead of what the user requested.
Reported-by: Thomas Haller <thaller@redhat.com>
Fixes: 1ec010e7 ("tun: export flags, uid, gid, queue information over netlink")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -2564,6 +2564,9 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 			 */
 			return 0;
 		}
+
+		tun->flags = (tun->flags & ~TUN_FEATURES) |
+			      (ifr->ifr_flags & TUN_FEATURES);
 	}
 	else {
 		char *name;
@@ -2642,6 +2645,9 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 				     ~(NETIF_F_HW_VLAN_CTAG_TX |
 				       NETIF_F_HW_VLAN_STAG_TX);
 
+		tun->flags = (tun->flags & ~TUN_FEATURES) |
+			      (ifr->ifr_flags & TUN_FEATURES);
+
 		INIT_LIST_HEAD(&tun->disabled);
 		err = tun_attach(tun, file, false, ifr->ifr_flags & IFF_NAPI);
 		if (err < 0)
@@ -2656,9 +2662,6 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 
 	tun_debug(KERN_INFO, tun, "tun_set_iff\n");
 
-	tun->flags = (tun->flags & ~TUN_FEATURES) |
-		(ifr->ifr_flags & TUN_FEATURES);
-
 	/* Make sure persistent devices do not get stuck in
 	 * xoff state.
 	 */