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>

fs/nfsd/nfs4xdr.c

@@ -1636,6 +1636,7 @@ static void encode_seqid_op_tail(struct nfsd4_compoundres *resp, __be32 *save, _
 			  (char *)resp->p - (char *)save;
 		memcpy(stateowner->so_replay.rp_buf, save,
 			stateowner->so_replay.rp_buflen);
+		nfsd4_purge_closed_stateid(stateowner);
 	}
 }