bgpd: RFC compliance wrt invalid RMAC, GWIP, ESI and VNI

bgpd: RFC compliance wrt invalid RMAC, GWIP, ESI and VNI

A route where ESI, GW IP, MAC and Label are all zero at the same time SHOULD
be treat-as-withdraw.
Invalid MAC addresses are broadcast or multicast MAC addresses. The route
MUST be treat-as-withdraw in case of an invalid MAC address.

As FRR support Ethernet NVO Tunnels only.
Route will be withdrawn when ESI, GW IP and MAC are zero or Invalid MAC

Test cases:
1) ET-5 route with valid RMAC extended community
2) ET-5 route no RMAC extended community
3) ET-5 route with Multicast MAC in RMAC extended community
4) ET-5 route with Broadcast MAC in RMAC extended community

Signed-off-by: Kishore Aramalla <karamalla@vmware.com>