ip6_gre: use exit_batch_rtnl() method

exit_batch_rtnl() is called while RTNL is held,
and devices to be unregistered can be queued in the dev_kill_list.

This saves one rtnl_lock()/rtnl_unlock() pair
and one unregister_netdevice_many() call.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Antoine Tenart <atenart@kernel.org>
Link: https://lore.kernel.org/r/20240206144313.2050392-11-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv6/ip6_gre.c

@@ -1632,21 +1632,19 @@ static int __net_init ip6gre_init_net(struct net *net)
 	return err;
 }
 
-static void __net_exit ip6gre_exit_batch_net(struct list_head *net_list)
+static void __net_exit ip6gre_exit_batch_rtnl(struct list_head *net_list,
+					      struct list_head *dev_to_kill)
 {
 	struct net *net;
-	LIST_HEAD(list);
 
-	rtnl_lock();
+	ASSERT_RTNL();
 	list_for_each_entry(net, net_list, exit_list)
-		ip6gre_destroy_tunnels(net, &list);
-	unregister_netdevice_many(&list);
-	rtnl_unlock();
+		ip6gre_destroy_tunnels(net, dev_to_kill);
 }
 
 static struct pernet_operations ip6gre_net_ops = {
 	.init = ip6gre_init_net,
-	.exit_batch = ip6gre_exit_batch_net,
+	.exit_batch_rtnl = ip6gre_exit_batch_rtnl,
 	.id   = &ip6gre_net_id,
 	.size = sizeof(struct ip6gre_net),
 };