Changing ipv6 loopback addresses on the linecards to be on different …

…subnets and adding t2 as a supported topology in veos (sonic-net#3797)

In bgpd.main.conf.j2 in sonic-buildimage (http://github.com/Azure/sonic-buildimage/blob/master/dockers/docker-fpm-frr/frr/bgpd/bgpd.main.conf.j2#L77),
Ipv6 Loopback0 addresses are using a 64 bit mask. In t2 topology, we have 2 linecards, and we were assigning two different IPv6 addresses:

- fc00:10::1/128
- fc00:10::2/128

However, in bgpd.main.conf.j2 in sonic-buildimage (http://github.com/Azure/sonic-buildimage/blob/master/dockers/docker-fpm-frr/frr/bgpd/bgpd.main.conf.j2#L77),
ipv6 Loopback0 addresses are using a 64 bit mask. Thus, the route to the Loopback0 address of the remote linecard was being masked by the local Loopback0 address,
and not pointing to the inband port.

Fix for this is to use different subnets for each linecard. So, changing the Loopback0 addresses to:
- fc00:10::1/128
- fc00:11::1/128

Also, t2 topology was missing from veos as a supported topology

ansible/vars/topo_t2-vs.yml

@@ -31,7 +31,7 @@ topology:
         - 10.1.0.2/32
       ipv6:
         - FC00:10::1/128
-        - FC00:10::2/128
+        - FC00:11::1/128
     vs_chassis:
       inband_port:
         - 30

ansible/vars/topo_t2.yml

@@ -326,8 +326,8 @@ topology:
         - 10.1.0.3/32
       ipv6:
         - FC00:10::1/128
-        - FC00:10::2/128
-        - FC00:10::3/128
+        - FC00:11::1/128
+        - FC00:12::1/128
 
 configuration_properties:
   common:

ansible/veos

@@ -34,6 +34,7 @@ all:
           - tgen-t0-3
           - tgen-t1-3-lag
           - mgmttor
+          - t2
       children:
         server_1:
         server_2: