MB-7629: Allow different chunk threshold sizes for KV and KP nodes

Change-Id: Ibc5a727b45bbbba563a717f39ae636ec15f37501
Reviewed-on: http://review.couchbase.org/25140
Tested-by: Fulu Li <fulu@couchbase.com>
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>