Allow ns_proxy extensions to modify parent state

Change-Id: I19fad853b632438f33950d210c98d4f0254d243e
Reviewed-on: http://review.couchbase.org/36022
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>