[Fullstack] L3 agent should be run in host namespace, together with L2 agent

[Slawek Kaplonski]

In fullstack tests L3 agent is not running in host namespace currently. That works fine e.g. with Linuxbridge agent, which is spawned in host-XXX namespace when test is creating and connecting FakeVM as it is always done in this host namespace and agent can see it.
However in case of using L3 agent this won't work because L3 agent creates veth connection between qrouter- namespace and global scope (no namespace) so linuxbridge agent can't see such tap device and is not creating proper network configuration for such router interfaces.