Comment 3 for bug 1802373

After more investigation, the problem is that the intermediate network ports get created as normal ports and then added to the router. When added to the router they get their owner changed to network:router so become trusted ports. networking-ovn doesn't honour this change of owner and they remain in the default drop port group so all the traffic is dropped.

If another port existed in such network, the Logical Flows corresponding to stateful (allow-related) ACLs get installed and traffic works.

The proper fix is patch the update_port method to honour changes to port owner.