network: enable LLDP for links that use only link-local addressing

network: enable LLDP for links that use only link-local addressing

Links with link-local-only communication are typically peer-to-peer
links between two laptops or similar. In such cases it makes sense to be
able to see which device one is specifically connected to, hence let's
just enable LLDP for it. This doesn't leak any data really, given that
this is inherently local, and typically only used between isolated
systems that are under the same user's possession.

Background: I recently connected multiple laptops via thunderbolt networking
and was kinda annoyed not being able to see what system I was actually
talking to.

(Also, the file touched here is an example only anyway, so even if this
would leak too much info, it's not in effect by default)