Support flow processing for layer-2 forwarded pkts

Agent changes to support flow processing for layer-2 forwarded packets
Packet is considered layer-2 forwarded packet if,
       1. Packet comes from VM Port and DMAC is not vrrp-mac
       2. Layer2-tunneled packet comes from fabric and DMAC is not same
          as phyiscal port

Flow still has IP 5-Tuple fields as the key
Basic UT for flow-processing

Change-Id: Iccf5d7e69e69cd8f5dca5579f6c54efaa7dc1b81

Conflicts:
	src/vnsw/agent/pkt/pkt_flow_info.cc
Add support for Layer-2 Receive Routes

Add support for L2-Receive NH
Add Layer-2 Receive routes for VRRP mac-address and mac-address on the
physical interface

Change-Id: I3c55b50ef562d696b620b1ee7245bc0cd7c2cd8a