NFSv4.1: Use session max response size for GETDEVICEINFO gdia_maxcount

We prepare for the largest possible GETDEVICEINFO response, which
can not be greater than the negotiated session maximum response size.

Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>