Increase max restarts for ns_child_ports_sup.

Since all the ports are restarted with delay of 5 seconds, it's enough
to have two ports constantly crashing to cause max restart intensity
with the old value.

Change-Id: I83cfe4c1c948e579533083eaf9c1b3d445a5cb8a
Reviewed-on: http://review.couchbase.org/35576
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>