Comment 0 for bug 1636654

Implement EVPN Type 5 infrastructure based on the following draft:

https://tools.ietf.org/html/draft-ietf-bess-evpn-prefix-advertisement-03

The scenario of interest is Interface-less IP-VRF-to-IP-VRF model
as described in section 5.4.1.

Hence we expect ESI and GW address fields to be all zero for now.