NFS: Fix bad defines of callback response maxsize

As CB_OP_TAGLEN_MAXSZ, all XXX_MAXSZ should be defined as bit.
Each operation should not cantains CB_OP_TAGLEN_MAXSZ.

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>