Description of problem:
Client is testing OVS to OVN migration.
They deploy a cloud with OVS.
Create instances.
Migrate to OVN.
Create new instances.

But then when trying IPv6 ping between old and new instances on the same compute node, it work only from old to new but not from new to old.

Could it be related to those BZ:
https://bugzilla.redhat.com/show_bug.cgi?id=2092463
[BUGZILLA] migration: stale ip6tables rules after migration | Product: Red Hat OpenStack | Component: python-networking-ovn | Version: 16.2 (Train) | Importance: urgent high |  Status: ON_DEV | Assigned to: Jakub Libosvar | Reported: 2022-06-01 15:38:53 +0000 | Modified: 2022-06-01 21:51:52 +0000

https://bugzilla.redhat.com/show_bug.cgi?id=2092472
[BUGZILLA] migration: stale ip6tables rules after migration | Product: Red Hat OpenStack | Component: openstack-neutron | Version: 16.2 (Train) | Importance: urgent high |  Status: NEW | Assigned to: OSP Team | Reported: 2022-06-01 16:16:08 +0000 | Modified: 2022-06-01 16:23:27 +0000


If you need anything else to debug this please let us know.

Thank you!


Version-Release number of selected component (if applicable):
OSP16.2.1 with those extra packages:
python3-networking-ovn-7.4.2-2.20220409154848.el8ost.noarch.rpm
python3-networking-ovn-migration-tool-7.4.2-2.20220409154848.el8ost.noarch.rpm

How reproducible:
100%

Steps to Reproduce:
1> Cloud deployed with OVS ml2. 
2> Create instances
3> Cloud migrated to OVN
4> Create new instances.
5> Try to ping between instances on the same compute nodes

Actual results:
IPv6 ping from new to old instance doesn't work

Expected results:
IPv6 ping work.

Additional info:
sosreport from compute node where the instance are running.