ELAN stale flow issue during VM migration

ELAN stale flow issue during VM migration

1) removing VpnPortIpToPort Listener in ELAN

* ELAN used to listen to VPNPortIptoPort data store
  for programming flows for MACs related to learnt IPs
* This is redundant since ELAN learns MAC by itself through table 50
* And this listener code could possibly lead to race
  conditions during VM migration leading to stale flows.

2) Fix for stale table 52 flows during migration

Removing the method createElanInterfaceTablesList to avoid
'modifiedNodeDoesNotExistException' when VM is migrated
from one DPN to another DPN, and delete and add ELAN
interface tries to update the same ElanInterfaceTablesList DS
improperly.

Signed-off-by: Amitesh Soni <amitesh.soni@ericsson.com>
Change-Id: Ib7ff56a89042362a74c6b8a241e1b2073b68d320