sit: allow to use rtnl ops on fb tunnel

rtnl ops where introduced by ba3e3f50 ("sit: advertise tunnel param via
rtnl"), but I forget to assign rtnl ops to fb tunnels.

Now that it is done, we must remove the explicit call to
unregister_netdevice_queue(), because  the fallback tunnel is added to the queue
in sit_destroy_tunnels() when checking rtnl_link_ops of all netdevices (this
is valid since commit 5e6700b3 ("sit: add support of x-netns")).
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/sit.c

@@ -1666,6 +1666,7 @@ static int __net_init sit_init_net(struct net *net)
 		goto err_alloc_dev;
 	}
 	dev_net_set(sitn->fb_tunnel_dev, net);
+	sitn->fb_tunnel_dev->rtnl_link_ops = &sit_link_ops;
 	/* FB netdevice is special: we have one, and only one per netns.
 	 * Allowing to move it to another netns is clearly unsafe.
 	 */
@@ -1700,7 +1701,6 @@ static void __net_exit sit_exit_net(struct net *net)
 
 	rtnl_lock();
 	sit_destroy_tunnels(sitn, &list);
-	unregister_netdevice_queue(sitn->fb_tunnel_dev, &list);
 	unregister_netdevice_many(&list);
 	rtnl_unlock();
 }