Fullstack Legacy L3 agent tests are failing very often recently

[Slawek Kaplonski]

Examples of the failures:

https://a3e9d176bf1a926ac6c8-4a42abeb7e7779ef25c6242290fc9b63.ssl.cf5.rackcdn.com/795185/1/check/neutron-fullstack-with-uwsgi/f7a1672/testr_results.html

https://storage.gra.cloud.ovh.net/v1/AUTH_dcaab5e32b234d56b626f72581e3644c/zuul_opendev_logs_7f5/788510/7/check/neutron-fullstack-with-uwsgi/7f51cfa/testr_results.html

https://storage.bhs.cloud.ovh.net/v1/AUTH_dcaab5e32b234d56b626f72581e3644c/zuul_opendev_logs_d7d/794777/1/check/neutron-fullstack-with-uwsgi/d7d7ad5/testr_results.html

https://13421bfde193d16eadd9-09dae87d9b597faab95a4d42e1ed51da.ssl.cf5.rackcdn.com/792953/3/check/neutron-fullstack-with-uwsgi/600701b/testr_results.html

In the neutron server logs I see errors like:

2021-06-08 04:28:04.056 137352 ERROR neutron_lib.callbacks.manager [req-1d1eba43-5cb8-49cc-8171-f914739630b1 - - - - -] Error during notification for neutron.plugins.ml2.ovo_rpc._ObjectChangeHandler.handle_event-4064702 port, after_create: TypeError: handle_event() missing 1 required positional argument: 'context'
2021-06-08 04:28:04.056 137352 ERROR neutron_lib.callbacks.manager Traceback (most recent call last):
2021-06-08 04:28:04.056 137352 ERROR neutron_lib.callbacks.manager File "/home/zuul/src/opendev.org/openstack/neutron/.tox/dsvm-fullstack-gate/lib/python3.8/site-packages/neutron_lib/callbacks/manager.py", line 197, in _notify_loop
2021-06-08 04:28:04.056 137352 ERROR neutron_lib.callbacks.manager callback(resource, event, trigger, **kwargs)
2021-06-08 04:28:04.056 137352 ERROR neutron_lib.callbacks.manager TypeError: handle_event() missing 1 required positional argument: 'context'
2021-06-08 04:28:04.056 137352 ERROR neutron_lib.callbacks.manager
2021-06-08 04:28:04.085 137352 DEBUG neutron.scheduler.dhcp_agent_scheduler [req-1d1eba43-5cb8-49cc-8171-f914739630b1 - - - - -] Network 08e13e32-a5ef-4045-9c91-403737ffea99 is already hosted by enough agents. _get_dhcp_agents_hosting_network /home/zuul/src/opendev.org/openstack/neutron/neutron/scheduler/dhcp_agent_scheduler.py:275

[Mamatisa Nurmatov (isabek)]

Hi @Slawek! For this logs a reported new bug here: https://bugs.launchpad.net/neutron/+bug/1931220 .
Uploaded fix: https://review.opendev.org/c/openstack/neutron/+/795260