nfsd: register NFS_ACL with rpcbind

Modify the NFS server to register the NFS_ACL services with the rpcbind
daemon.  This allows the client to ping for the existence of the NFS_ACL
support via commands such as "rpcinfo -t <server> nfs_acl".

This patch also modifies the NFS_ACL support so that responses to
version 2 NULLPROC requests can be made.

The changelog for the patch which turned off this functionality
mentioned something about not registering the NFS_ACL as being part of
some tradition.  I can't find this tradition and the only other
implementation which supports NFS_ACL does register them with the
rpcbind daemon.

Signed-off-by: Peter Staubach <staubach@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
diff --git a/fs/nfsd/nfs3acl.c b/fs/nfsd/nfs3acl.c
index 9981dbb..ff73596 100644
--- a/fs/nfsd/nfs3acl.c
+++ b/fs/nfsd/nfs3acl.c
@@ -264,6 +264,6 @@
 		.vs_proc	= nfsd_acl_procedures3,
 		.vs_dispatch	= nfsd_dispatch,
 		.vs_xdrsize	= NFS3_SVC_XDRSIZE,
-		.vs_hidden	= 1,
+		.vs_hidden	= 0,
 };