net: Convert pg_net_ops

These pernet_operations create per-net pktgen threads
and /proc entries. These pernet subsys looks closed
in itself, and there are no pernet_operations outside
this file, which are interested in the threads.
Init and/or exit methods look safe to be executed
in parallel.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/pktgen.c

@@ -3851,6 +3851,7 @@ static struct pernet_operations pg_net_ops = {
 	.exit = pg_net_exit,
 	.id   = &pg_net_id,
 	.size = sizeof(struct pktgen_net),
+	.async = true,
 };
 
 static int __init pg_init(void)