NFSv4.2: Clean up xattr size macros

Fold them into the other NFS v4.2 operations in the right spots and
adjust spacing to keep the same style.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>