For DHCP relay support, and possibly other features, there is a need to
add specific allow rules to the router firewall between the FWaas v1/v2
rules, and the default drop rule.
This patch set the structure to do that, without actually adding new rules.
In case of FWaaS v2 the additional rules are per router interface.
Change-Id: I63d754495f56ec9081d84dcea6fb688ee1c41dbd
afdb9ea7ac