Enable transfers over link scoped addresses

[mweinelt]

Currently, the if-addrs crate is used without the link-local feature so link scoped addresses are not part of the advertisement.

Using link scoped addresses makes sense for local delivery (e.g. same WLAN, LAN, but also a direct Thunderbolt network link), without relying on routable addresses.

When receiving a link scoped address (fe80::/64), try connecting over all local links, that have a link-local addresses configured to discover the peer.