rtnetlink: fix netns leak with rtnl_setlink()

A call to rtnl_nets_destroy() is needed to release references taken on
netns put in rtnl_nets.

CC: stable@vger.kernel.org
Fixes: 636af13 ("rtnetlink: Register rtnl_dellink() and rtnl_setlink() with RTNL_FLAG_DOIT_PERNET_WIP.")
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250205221037.2474426-1-nicolas.dichtel@6wind.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/rtnetlink.c

@@ -3432,6 +3432,7 @@ static int rtnl_setlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 		err = -ENODEV;
 
 	rtnl_nets_unlock(&rtnl_nets);
+	rtnl_nets_destroy(&rtnl_nets);
 errout:
 	return err;
 }