MB-100 Maintain queue_operation field as uint16_t in QueuedItem
MB-100 Maintain queue_operation field as uint16_t in QueuedItem

As we extend seq_num field to 64 bits, it would be better to
pack queue_operation as uint16_t in QueuedItem class.

Change-Id: I3be2b527e988eae9616ba8c0969583b30d02c37c
Reviewed-on: http://review.couchbase.org/18311
Reviewed-by: Liang Guo <863407acb9e207441ec9e80d0debd4fe4489aa9b@couchbase.com>
Tested-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>

abhinavdangeti/ep-engine,owendCB/ep-engine,daverigby/kv_engine,daverigby/ep-engine,sriganes/ep-engine,sriganes/ep-engine,hisundar/ep-engine,sriganes/ep-engine,couchbase/ep-engine,daverigby/ep-engine,owendCB/ep-engine,daverigby/kv_engine,membase/ep-engine,owendCB/ep-engine,daverigby/kv_engine,jimwwalker/ep-engine,abhinavdangeti/ep-engine,abhinavdangeti/ep-engine,teligent-ru/ep-engine,owendCB/ep-engine,jimwwalker/ep-engine,couchbase/ep-engine,couchbase/ep-engine,membase/ep-engine,membase/ep-engine,abhinavdangeti/ep-engine,membase/ep-engine,jimwwalker/ep-engine,daverigby/ep-engine,daverigby/ep-engine,jimwwalker/ep-engine,hisundar/ep-engine,hisundar/ep-engine,couchbase/ep-engine,sriganes/ep-engine,teligent-ru/ep-engine,teligent-ru/ep-engine,daverigby/kv_engine,teligent-ru/ep-engine,abhinavdangeti/ep-engine,hisundar/ep-engine