MB-100: replace dirty ns_port_sup access with use of new API

Change-Id: I05f779f819b4c37a56f60aea8fb57b6e725cbabd
Reviewed-on: http://review.couchbase.org/25476
Tested-by: buildbot <build@couchbase.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Ketaki Gangal <ketakigangal@gmail.com>