Comment 3 for bug 1915856

Expected behavior is incorrect. Port update must succeed, without updating Placement allocation record. This is critical, as not all users use Placement enforcement, but they still expect dataplane enforcement to happen. This behavior is described in [1]. Relevant part:

"As it is possible to update a port to remove the QoS policy, updating it back to have QoS policy with minimum_bandwidth rule will not result in placement allocation record, only the dataplane enforcement will happen."

This issue was fixed in [2], which deletes allocation key in the port binding when QoS policy is set to None.

[1] https://opendev.org/openstack/neutron/src/branch/master/doc/source/admin/config-qos-min-bw.rst#L77
[2] https://review.opendev.org/c/openstack/neutron/+/805637