always update snapshot seqno on upr rollback

Previously in path where we work around upr inconvenience and rollback
volunarily we did not actually update snaphost seqno. Causing snapshot
seqno to be greater than data seqno.

Change-Id: Iaee48131c4aafdd9ddea67f6e42de04d05e755a4
Reviewed-on: http://review.couchbase.org/35025
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>