With the new feature implemented in [1], some resources are not directly managed by the Neutron API. In this case, there are ``Logical_Routers`` that are created by some extensions (ovn-bgp [2]) that don't have the corresponding Neutron router ID (the field ``ovn_const.OVN_ROUTER_NAME_EXT_ID_KEY`` in the external_ids column).

It is needed that the event ``LogicalRouterPortEvent`` discards the events received from ``Logical_Router_Ports`` that belong to this kind of "not managed" resources.

These errors were found in the still not merged patch [3], that is testing the implementation of the "ovn-bgp" extension in ML2/OVN.

Error snippet (from [3], in the Neutron API logs): https://paste.opendev.org/show/boOE7g8g4Id7iXLC3Os3/

U/S launchpad bug: https://bugs.launchpad.net/neutron/+bug/2139067

[1]https://review.opendev.org/q/topic:%22bug/2111276%22
[2]https://review.opendev.org/c/openstack/neutron/+/963223/11/neutron/services/bgp/commands.py
[3]https://review.opendev.org/c/openstack/neutron/+/962188