Comment 2 for bug 1896913

This is basically bug by bug compatibility with the neutron-openvswitch and neutron-gateway charms.

The issue is similar to bug 1872799 but not quite the same as OVN allows you to get DVR-like functionality without having bridge mappings configured for all units.

The charm could definitively give more friendly feedback than going into a hook error for non-existing ports, and it would also be useful to update the workload message with information about chassis being configured for use as a gateway or not.