ELAN: VNI support in datapath for VxLAN networks

ELAN: VNI support in datapath for VxLAN networks

This commit adds support for VNI based datapath forwarding for VxLAN
based provider networks.
Spec: https://git.opendaylight.org/gerrit/#/c/48640/

a. Unicast
  1. Table 51 now sets VNI in tun_id field for packets egressing on
     tunnel ports
  2. On egress, table 36 now matches on VNI in tun_id field, sets the
     ELAN tag in metadata, and forwards the traffic to table 51

b. Broadcast
  1. Remote broadcast group now sets VNI in tun_id field for packets
     egressing on tunnel ports
  2. On egress, table 36 now matches on VNI in tun_id field, sets the
     ELAN tag in metadata, and forwards the traffic to table 51

Also, integrates the openstack-vni-semantics-enforced flag to enable
easier turning on/off of the feature

Change-Id: I7a6b14897344a8d00cb19291602d92cf586f15f7
Signed-off-by: Abhinav Gupta <abhinav.gupta@ericsson.com>