Retain forward/reverse flow semantics if flow is already present

    Conflicts:
        src/vnsw/agent/pkt/pkt_flow_info.cc

    Change-Id: I713711760516ab9e04a3e82084e7ed7a6d0cc28d

Change-Id: I356bfac036c2bea855e599f7b539a1cd9b0c7947