Neutron to Drop Router Advts from VM ports

Neutron to Drop Router Advts from VM ports

As part of Spoofing filter chain Neutron drops all the outbound
traffic where MAC/IP does not match the IP address assigned
to the VM ports (inc' allowed_address_pairs). Along with this,
we also drop traffic associated to dhcp[v6] server (i.e., do
not allow a VM to run dhcp[v6] server). Currently we do not
have any rules to drop Router Advts from VM ports. This can create
issues in the network as other devices in the network may not have
any protection for this kind of stuff.

Even if we allow RAs from the VM ports, because of the Anti-Spoofing
rules that are applied, a VM cannot act as a IPv6 router (i.e., it
cannot forward IPv6 traffic). So there is no point in allowing Router
Advts from VMs assuming that it would be useful in Service VM use-cases.
In order to properly implement IPv6 router as a Service VM, one needs
to use the port_security_extension [1] which allows us to disable
security group rules/anti-spoofing filters on the VM ports.

[1]https://review.openstack.org/#/c/99873/22/specs/kilo/ml2-ovs-portsecurity.rst

This patch disables Router Advts from VM ports.

Closes-Bug: #1372882
Change-Id: I8db5d6dbe60bf04f4e3754a886c6aa8a97a16bab