Comment 1 for bug 1821150

The flat network is configured as 'public' in ovs agent's config file ml2_conf.ini:
   [ml2_type_flat]
   flat_networks = public

Creating flat provider network 'providernet-a' can't change the configuration.

You can check the configuration by following command on the active controller:
   export OS_CLOUD=openstack_helm
   kubectl -n openstack get pod | grep neutron
   kubectl -n openstack exec -it ${neutron-ovs-agent} bash
   cd /etc/neutron/plugins/ml2/
   cat ml2_conf.ini