net: Convert uevent_net_ops

uevent_net_init() and uevent_net_exit() create and
destroy netlink socket, and these actions serialized
in netlink code.

Parallel execution with other pernet_operations
makes the socket disappear earlier from uevent_sock_list
on ->exit. As userspace can't be interested in broadcast
messages of dying net, and, as I see, no one in kernel
listen them, we may safely make uevent_net_ops async.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

lib/kobject_uevent.c

@@ -650,6 +650,7 @@ found:
 static struct pernet_operations uevent_net_ops = {
 	.init	= uevent_net_init,
 	.exit	= uevent_net_exit,
+	.async  = true,
 };
 
 static int __init kobject_uevent_init(void)