nfsd41: use session maxreqs for sequence target and highest slotid

This fixes a bug in the sequence operation reply.

The sequence operation returns the highest slotid it will accept in the future
in sr_highest_slotid, and the highest slotid it prefers the client to use.
Since we do not re-negotiate the session slot table yet, these should both
always be set to the session ca_maxrequests.

Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>