NFS: use dynamically computed compound_hdr.replen for xdr_inline_pages offset

As Trond suggested, rather than passing a constant to xdr_inline_pages,
keep a running count of the expected reply bytes.  In preparation for
nfs41, where additional op sequence are expteced when talking to nfs41
servers.

[NFS: cb_compoundhdr.replen is in words not bytes]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
[nfs41: get fs_locations replen before encoding the GETATTR]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
[nfs41: get getacl replen before encoding the GETATTR]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>