Unable to detect from OVN DB if Neutron uses distributed floating IPs or not

[Jakub Libosvar]

Actually I don't know if this should be an RFE or a bug.

Previously Neutron set external_mac in a NAT entry if the floating IP was distributed and it was left unset if the traffic was centralized. Nowadays, the behavior is inconsistent and external_mac is set after the port associated with the FIP transitions to the UP state - meaning that while the port is down, we are not able to say if the traffic will be distributed or not.

It would be good to have this configuration option stored at one place - for example NB_Global.external_ids column can store a value for distributed routing since it's a global option for the whole Neutron. There are projects, like ovn-bgp-agent that could use this information before-hand so the agent knows if the floating IP should be exposed on the compute node or on the network node.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/neutron/+/931067