NFSv4.1: Ensure smooth handover of slots from one task to the next waiting

Currently, we see a lot of bouncing for the value of highest_used_slotid
due to the fact that slots are getting freed, instead of getting instantly
transmitted to the next waiting task.

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

diff --cc fs/nfs/nfs4proc.c
Simple merge

diff --cc fs/nfs/nfs4session.c
Simple merge

diff --cc fs/nfs/nfs4session.h
Simple merge

diff --cc fs/nfs/nfs4state.c
Simple merge