Bug reproduced on RHOSO 18 using either live or cold migration.

The following WNTP tests reproduce it: test_qos_after_live_migration and test_qos_after_cold_migration
https://opendev.org/x/whitebox-neutron-tempest-plugin/src/branch/master/whitebox_neutron_tempest_plugin/tests/scenario/test_qos.py

The manual reproduction is quite simple:

1. create a VM with a port from a VLAN tenant network
2. add a QoS policy with BW limit to that network
3. check on OVN NB DB that the BW limit has been applied to the VM's LSP (see example [1])
4. migrate (either live or cold) that VM to a different compute
5. check on OVN NB DB that the BW limit has not been changed on the VM's LSP. This currently fails because the max_rate and burst options are removed after the migration (see example [2])

This is a regression because this didn't fail with previous RHOSO versions. It seems behavior has changed due to OSPRH-11045.

[1] 

[zuul@controller-0 ~]$ oc rsh ovsdbserver-nb-0 ovn-nbctl --no-leader get logical_switch_port 3a9223f4-397b-4919-8d00-7571c1e036f4 options
{qos_burst="800000", qos_max_rate="1000000", requested-chassis=compute-zyei6xva-0.ctlplane.example.com} 

[2] 

[zuul@controller-0 ~]$ oc rsh ovsdbserver-nb-0 ovn-nbctl --no-leader get logical_switch_port 3a9223f4-397b-4919-8d00-7571c1e036f4 options
{requested-chassis=compute-zyei6xva-1.ctlplane.example.com}