Re-enable IPv6Test in OVN scenario job

The related bug is fixed in ovn with[1], so issue
should not be see with ovn-20.03.2+ releases. This
patch re-enables the test by removing it from blacklist,
and adding it to ussuri ovn job as that is running with
ovn-20.03.0.

[1] https://github.com/ovn-org/ovn/commit/53285ae

Depends-On: https://review.opendev.org/c/openstack/networking-sfc/+/827410/
Related-Bug: #1881558
Change-Id: I73c3d6caeaf578fb032750c34e1aaa1ac041da9a
2 files changed