MB-11259: Buffer acknowledgment should have extlen of 4
MB-11259: Buffer acknowledgment should have extlen of 4

Change-Id: I2b22316e876a81211fe1cf676cb4f8c531162145
Reviewed-on: http://review.couchbase.org/37764
Reviewed-by: Michael Wiederhold <a17fed27eaa842282862ff7c1b9c8395a26ac320@couchbase.com>
Tested-by: Michael Wiederhold <a17fed27eaa842282862ff7c1b9c8395a26ac320@couchbase.com>

owendCB/memcached,mrkwse/memcached,mrkwse/memcached,cloudrain21/memcached-1,cloudrain21/memcached-1,couchbase/memcached,daverigby/kv_engine,jimwwalker/memcached,daverigby/kv_engine,daverigby/kv_engine,couchbase/memcached,couchbase/memcached,daverigby/memcached,cloudrain21/memcached-1,mrkwse/memcached,jimwwalker/memcached,daverigby/memcached,jimwwalker/memcached,daverigby/memcached,daverigby/kv_engine,owendCB/memcached,owendCB/memcached,couchbase/memcached,owendCB/memcached,mrkwse/memcached,cloudrain21/memcached-1,daverigby/memcached