fixing test_pkt_flow memory leak and test case failure.

We should not skip a delete message for flow in any case other than
flow index invalid. so moving the check for reverse flow index to
Add/Change operation only.(fixes above mentioned test case failure)

Change-Id: Ibf7225a612fa454ff9f9145fa4a8b15c1ef0c5fe
Merge "fixing test_pkt_flow memory leak and test case failure."