nfsd41: Backchannel: cleanup nfs4.0 callback encode routines

Mimic the client and prepare to share the back channel xdr with NFSv4.1.
Bump the number of operations in each encode routine, then backfill the
number of operations.

Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Ricardo Labiaga <Ricardo.Labiaga@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>