Feature: --libp2p-port and ---libp2p-port-ipv6 identical by default

[yorickdowne]

Description

Currently, the --libp2p-port and --libp2p-port-ipv6` options have distinct default values

This means additional configuration steps for users, whether for ufw or host-mapped docker ports.

Feature suggestion

From a networking perspective, the ports could be the same and a program could listen on v4 and v6. This is the standard behavior for dual-stack applications.

Ditto for --discovery-port and --quic-port

This does work for Grandine when configured that way: I am suggesting to make it the default.