NFSD: Update XDR decoders in NFSv4 callback client

Clean up.

Remove old-style NFSv4 XDR macros in favor of the style now used in
fs/nfs/nfs4xdr.c.  These were forgotten during the recent nfs4xdr.c
rewrite.

Additional whitespace cleanup adds to the size of this patch.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>