net: Convert nfs4blocklayout_net_ops

These pernet_operations create and destroy per-net pipe
and dentry, and they seem safe to be marked as async.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Anna Schumaker <Anna.Schumaker@netapp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

fs/nfs/blocklayout/rpc_pipefs.c

@@ -261,6 +261,7 @@ static void nfs4blocklayout_net_exit(struct net *net)
 static struct pernet_operations nfs4blocklayout_net_ops = {
 	.init = nfs4blocklayout_net_init,
 	.exit = nfs4blocklayout_net_exit,
+	.async = true,
 };
 
 int __init bl_init_pipefs(void)