nfsd: report in /proc/fs/nfsd/clients/*/states when state is admin-revoke

Add "admin-revoked" to the status information for any states that have
been admin-revoked.  This can be useful for confirming correct
behaviour.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>