nfsd4: match close replays on stateid, not open owner id

Keep around an unhashed copy of the final stateid after the last close
using an openowner, and when identifying a replay, match against that
stateid instead of just against the open owner id.  Free it the next
time the seqid is bumped or the stateowner is destroyed.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>