As the (removed) comment said, this was a one-time-hack that was obsoleted long ago.

Also move it to gluon-mesh-batman-adv, as mesh_on_wan is the only feature that
needs a unique MAC address on the WAN interface.

The now empty gluon-firewall is removed.

The support is still very limited (IPv6-only DNS on WAN doesn't work yet), and
we now need fastd running as root, but apart from that, is should work.

As we don't have any older gluon versions so far, and hope to be able to do all
upgrades with invariant scripts, remove the code for now.

If we ever see the need to add such upgrade scripts, we can just re-add this.

In combination with kernel.panic the node will reboot if out of memory.