Blocks #581 attempt of solution in #631

tl;dr without VLAN, Babeld currently cannot run on ethernet

When instructing Babeld to run on the plain interfaces, without any VLAN, it fails to run on LAN ethernet ports.
The reason is that they lack an IPv6 Link Local address, and they cannot have it as they are included in br-lan bridge.

So, just in the case of Babeld witout VLAN, we should run it directly over the br-lan bridge.

The problem is that Batman-adv interface is also into the bridge and to have hello packets of Babeld running into Batman-adv would completely break Babeld topology estimation.

So some firewall rules like the ones in lime-proto-bmx6 here will have to be used.