nfsd: Do not try to cache a reply for NFSERR_BADSLOT

When nfsrv_checksequence() replies NFSERR_BADSLOT,
the value of nd_slotid is not valid. As such, the
reply cannot be cached in the session.
Do not set ND_HASSEQUENCE for this case.

Reported by: rtm@lcs.mit.edu
Tested by: rtm@lcs.mit.edu
PR: 260076
MFC after: 2 weeks