MB-11887: Properly send the snapshot start and end seqnos

Currently we always set the snapshot start and end seqno to be the
same as the start seqno. This is incorrect if we recently were
disconnected and need to resume from a partial snapshot.

Change-Id: I7c9430e0b24ef01cc427cb03b518f4c41a55d875
Reviewed-on: http://review.couchbase.org/40276
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>