net: Convert sysctl_pernet_ops

This patch starts to convert pernet_subsys, registered
from core initcalls.

Methods sysctl_net_init() and sysctl_net_exit() initialize
net::sysctls table of a namespace.

pernet_operations::init()/exit() methods from the rest
of the list do not touch net::sysctls of strangers,
so it's safe to execute sysctl_pernet_ops's methods
in parallel with any other pernet_operations.

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

net/sysctl_net.c

@@ -89,6 +89,7 @@ static void __net_exit sysctl_net_exit(struct net *net)
 static struct pernet_operations sysctl_pernet_ops = {
 	.init = sysctl_net_init,
 	.exit = sysctl_net_exit,
+	.async = true,
 };
 
 static struct ctl_table_header *net_header;