consumer rss does not honour eventing memory quota for bucket op with small docs

Build 6.5.0-4788

Observed that even if eventing memory quota set as 24GB, consumer rss grows till 55GB when kv docs are of size 64 bytes.

Here are run details for 2 hours of access phase-

Job- http://perf.jenkins.couchbase.com/job/themis/4389

cbmonitor link- http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=themis_650-4788_load_access_and_wait_304a

Attached screenshot of consumer rss during the test.

This issue is not present in 6.5.0-3573, and present in 6.5.0-3607.

Job for 6.5.0-3607- http://perf.jenkins.couchbase.com/job/themis/4393

cbmonitor url for 6.5.0-3607- http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=themis_650-3607_load_access_and_wait_d0b9

We do not see this pattern when kv doc size is 1K, here is cbmonitor graph for 6.5.0-4821 build- http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=themis_650-4821_load_access_and_wait_4e5c

Change log between 6.5.0-3573 and 6.5.0-3607- http://172.23.123.43:8000/getchangelog?product=couchbase-server&fromb=6.5.0-3573&tob=6.5.0-3607