CSIT Sporadic failures - ipv6 tests failing in learn sg mode

four tempest.scenario.v6 tests have been added to CSIT recently. They are passing
when running in stateful and transparent sg modes, but fail in learn mode.

example log:
https://logs.opendaylight.org/releng/jenkins092/netvirt-csit-1node-openstack-newton-nodl-v2-upstream-learn-carbon/303/log.html.gz

debugging the tempest failures is not easy in this environment. We do have
non-tempest robot csit coming soon around v6 so maybe those will also hit
this same issue and we can debug more easily there.