harvester: replace fastd l2 backbone links with vxlan

[1977er]

roles/ffh.mesh_fastd/templates/backbone.conf.j2 curretly uses a mesh_fastd link to create a layer2 connection between a super(exit)node and harvester. We already replaced the supernode-supernode links with vxlan and should do the same with the connection to harvester.

Objections, ideas?

[AiyionPrime]

No objections.
As long as fastd nodes are still able to report their data to harvester.

[lemoer]

Go ahead. 👍