MB-9898: Upr consumer flow control code

Change-Id: Iba15280f6993fc1b67f089be087ea317f723a16b
Reviewed-on: http://review.couchbase.org/35419
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>