ONU disable/re-enable breaks SiaB

Building a SiaB using 'make latest' pulls in the latest VOLTHA 1.x Docker images and latest versions of ONOS apps.  On this SiaB, disabling and re-enabling the ONU results in the ONU being in ENABLED / ACTIVE / REACHABLE state but with no flows.  No traffic is passed after that point.

It appears that this problem may be specific to Ponsim, since QA reports that they don't see it on a hardware SEBA pod.

It is also the case that this problem does not show up in the context of VOLTHA atests that also use Ponsim.  I've tried manually altering the atests to perform a disable/re-enable cycle on the ONU prior to authentication and it works fine.