nfs: standardize the rename args container

Each NFS version has its own version of the rename args container.
Standardize them on a common one that's identical to the one NFSv4
uses.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>