net: Call preinit_net() without pernet_ops_rwsem.

When initialising the root netns, we call preinit_net() under
pernet_ops_rwsem.

However, the operations in preinit_net() do not require pernet_ops_rwsem.

Also, we don't hold it for preinit_net() when initialising non-root netns.

To be consistent, let's call preinit_net() without pernet_ops_rwsem in
net_ns_init().

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/net_namespace.c

@@ -1199,8 +1199,9 @@ void __init net_ns_init(void)
 #ifdef CONFIG_KEYS
 	init_net.key_domain = &init_net_key_domain;
 #endif
-	down_write(&pernet_ops_rwsem);
 	preinit_net(&init_net);
+
+	down_write(&pernet_ops_rwsem);
 	if (setup_net(&init_net, &init_user_ns))
 		panic("Could not setup the initial network namespace");