Recent NFS v4.2 drafts have removed NFS4ERR_METADATA_NOTSUPP and
reassigned the error code to NFS4ERR_UNION_NOTSUPP.

I also add in the NFS4ERR_OFFLOAD_NO_REQS error code.

We're not using any of these yet, so there's no harm done.
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>