Ignore router advertisements in PTF (sonic-net#20113)

Ignore any router advertisements sent by a DUT, and don't set a default
route or an address based on it. This could happen if a T0 testbed with
radv running sends router advertisements on a VLAN interface, which may
result in the PTF container adding a default route on all of the VLAN
interfaces. This could result in some IPv6 test cases breaking.

Signed-off-by: Saikrishna Arcot <sarcot@microsoft.com>

Author: saiarcot895

ansible/roles/vm_set/tasks/add_topo.yml

@@ -190,6 +190,10 @@
     command: docker exec -i ptf_{{ vm_set_name }} sysctl -w net.ipv6.route.max_size=168000
     become: yes
 
+  - name: Don't accept ipv6 router advertisements for docker container ptf_{{ vm_set_name }}
+    command: docker exec -i ptf_{{ vm_set_name }} sysctl -w net.ipv6.conf.default.accept_ra=0
+    become: yes
+
   - name: Create file to store dut type in PTF
     command: docker exec -i ptf_{{ vm_set_name }} sh -c 'echo {{ hostvars[duts_name.split(',')[0]]['type'] }} > /sonic/dut_type.txt'
     when: