nfsd41: encode replay sequence from the slot values

The sequence operation is not cached; always encode the sequence operation on
a replay from the slot table and session values. This simplifies the sessions
replay logic in nfsd4_proc_compound.

If this is a replay of a compound that was specified not to be cached, return
NFS4ERR_RETRY_UNCACHED_REP.

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