Fixes bug - 2505

- Avoid changing flow_handle from response for del ACK.
  for entry reuse case, this flow handle change will result in leaving hold
  entries in vrouter due to trying to program old flow handle
- Avoid compressing Add flowed by delete as no OP for flow, since we
  still need to delete the flow from vrouter.
- when the flow entry is reused, we need to trigger KSyncSM_Add instead of
  KSync_Change, so that the intial add message is not skipped for no change.
- adding test-cases.