Add missing extensible type registries

The following types were not setup to discover extensions

com.cloud.network.element.FirewallServiceProvider
com.cloud.network.element.PortForwardingServiceProvider
com.cloud.network.element.StaticNatServiceProvider
com.cloud.network.element.NetworkACLServiceProvider
com.cloud.network.element.LoadBalancingServiceProvider
com.cloud.network.element.Site2SiteVpnServiceProvider