Add support for inbound traffic on CNI/primary network interface

[solidDoWant]

Details

Describe the solution you'd like: This container is often used in conjunction with VPN containers. Some of them, like gluetun, support an HTTP health check endpoint. It would be nice if this tool allowed for opening additional inbound ports, so that k8s health checks can contact and talk to the VPN health endpoint.

Anything else you would like to add:

Additional Information: