net: Convert cma_pernet_operations

These pernet_operations just create and destroy IDR.
So, we mark them as async.

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

drivers/infiniband/core/cma.c

@@ -4549,6 +4549,7 @@ static struct pernet_operations cma_pernet_operations = {
 	.exit = cma_exit_net,
 	.id = &cma_pernet_id,
 	.size = sizeof(struct cma_pernet),
+	.async = true,
 };
 
 static int __init cma_init(void)