[BucketDurability]: Updated bucket durability level is not taken into effect immediately

Build: 6.6.0-7724

Steps to reproduce:

1. Two node cluster, Couchbase bucket(replicas=2, bucket_durability_level=None)
2. Update bucket durability using REST API
3. Immediately try a async_write from Java SDK client (Assuming the async_write will be promoted to sync_write internally)

Observation:

The attempted indirect sync_write was taken as async_write only.

]# /opt/couchbase/bin/cbstats -u Administrator -p password localhost:11210 vbucket-details 342 | grep committed

 vb_342:sync_write_committed_count: 0

Attempting a async_write after some time (say 10seconds) is resulting in incrementing the sync_write counter.

Server logs:

https://cb-jira.s3.us-east-2.amazonaws.com/logs/b_durability_sync_write_counter/collectinfo-2020-06-01T191826-ns_1%4010.112.191.101.zip
https://cb-jira.s3.us-east-2.amazonaws.com/logs/b_durability_sync_write_counter/collectinfo-2020-06-01T191826-ns_1%4010.112.191.102.zip

Attaching pcap bucket_d_update_with_client_error.pcapng for further debugging.