Standardizing default p2p ports

[wemeetagain]

RE: Validator privacy concerns mentioned in ethereum/eth2.0-pm#171

If client A and client B differ by their default ports, nodes on the network are easily sorted into client type based on port number alone.

Should the spec include a SHOULD default port for discv5 + libp2p?

[wemeetagain]

Somewhat related, eth2.0-metrics specifies a standard port: https://github.com/ethereum/eth2.0-metrics/blob/master/metrics.md#prometheus-metrics-collection

By default, the Prometheus collection endpoint SHOULD be served from 0.0.0.0:8008.

[jrhea]

RE: Validator privacy concerns mentioned in ethereum/eth2.0-pm#171

If client A and client B differ by their default ports, nodes on the network are easily sorted into client type based on port number alone.

Should the spec include a SHOULD default port for discv5 + libp2p?

I figured it wasn't worth deciding on until #2008 is figured out. If we ultimately decide that agent-string should be kept, then this privacy concern is a non-issue.

[djrtwo]

Also, sharing default ports has some emergent issues when people try to run multiple clients on same machine. Not really a huge issue on mainnet, but an annoyance

@benjaminion mentioned picking the same port as lighthouse as a "poor decision"

this was a poor decision on our part! Just didn't account for people running multiple clients on one machine. I expect it's more of a testnet phenomenon than long-term, but this seems to be our number 1 bump in the road right now.

[dapplion]

The ship has sailed here, each client has its own default port