autorelay: select relays based on latency

[vyzo]

With the planned deployment of relay infrastructure, it will make sense to select relays based on minimum latency.

Proposed action:

• Modify the autorelay relay selection strategy to select based on ping latency.

[vyzo]

cc @Stebalien

[Stebalien]

That sounds like a decent initial approach (we can try other benchmarks later).

[marten-seemann]

The problem here is that we don't want to flood relay nodes that happen to be very well connected to many other nodes with reservation requests.