MB-11941: Use the latest seqno during tap mutation/deletion cur snapshot

We generate the seqno when inserting the item into the hashtable when
using tap. As a reuslt we need to retrieve that seqno when updating
the latest snapshot because the byseqno passed into the mutation and
deletion functions for tap is always 0.

Change-Id: I21b7888207d9fea4f46b3d5918d1c8b60b2ea1ff
Reviewed-on: http://review.couchbase.org/40601
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>