If DHCP is disabled in config, flood DHCP requests in the VN

Change-Id: I81f27a921b1e88ba55dbf0b5ae2f6de0ce501dbe
* Add a flag in route to trap GARP packets hitting that route

Change-Id: Ifd77b2456b91104fe8c2eed5e5e45397fb76453a
- Changes to support cross connect without scripts
  - agent alive/dead detected based on addition of pkt0 vif and removal of
    pkt0 interface from the system (OS)
  - on agent's death, all vhost interface and their corresponding physical
    interfaces are put on cross connect mode where the traffic will still
    pass through vrouter
  - from the time of reset till vhost gets added back again, traffic moves
    directly from physical interface to vhost
  - once vhost interface is added, traffic flows normally through vrouter

Change-Id: I7cacebc5432347e11fc15213edd22f372cf6c9ef