When multiple ONUs on PON port, disable and re-enable of OLT does not work sometimes

When multiple ONUs on PON port, disable and re-enable of OLT does not work. One or more ONUs on the PON cannot DHCP and PING.

The steps in the test are as follows.

1. Two or more ONUs on a PON port.
2. ONU is active, reachable and in omci-flows-pushed state with subscriber s and c vlan configured. ONUs are able to DHCP and ping
3. OLT is disabled.
4. All the ONUs on the PON port are subscriber unprovsioned from ONOS
5. OLT is enabled.
6. subscriber is provisioned again
7. Trying DHCP and PING

Sometimes the ONUs cannot DHCP and ping.

The reason is when OLT is disabled, and subscriber unprovisioned, and this results in all the flows referencing the ONU getting removed. Then the olt adapter cleans up gem and tcont resource. But ONU adapter cannot communicate with the ONU device to do this cleanup as the ONU is unreachable (as OLT is disabled.). The stale resources remain in ONU. When is OLT is re-enabled again, there is fair chance that ONU may not get same gem PON resource IDs. The old and new resources get mixed up in the ONU device and create unpredictable behavior.

ONU should ensure proper cleanup of any old resources and related configuration before it starts downloading the TP again.