Neutron does not disable ipv6 forwarding for HA routers and it's
enabled by default in all router namespaces. For ipv6, this means
that it will automatically join the following groups:
* link-local all-routers multicast group (ff02::2)
* interface-local all routers multicast group (ff01::2)
* site-local all routers multicast group (ff05::2))
As a side effect it will answer to multicast listener queries, thus
causing external switch to learn its MAC address and disrupting traffic
to the master instance.
This patch will enable ipv6 forwarding on the gateway interface only
for master instances and disable it otherwise to fix the issue.
Also, the accept_ra procfs entry was enabled under certain
circumstances but it wasn't disabled otherwise. This patch, will
disable RA on the gateway interface for non master instances.
Closes-Bug: #1667756
Change-Id: I9bc890b43f750cad68fc67f4c79f1426c3506863
676a3ebe2f