net: Convert nfsd_net_ops

These pernet_operations look similar to rpcsec_gss_net_ops,
they just create and destroy another caches. So, they also
can be async.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

fs/nfsd/nfsctl.c

@@ -1263,6 +1263,7 @@ static struct pernet_operations nfsd_net_ops = {
 	.exit = nfsd_exit_net,
 	.id   = &nfsd_net_id,
 	.size = sizeof(struct nfsd_net),
+	.async = true,
 };
 
 static int __init init_nfsd(void)