Modernise this man page somewhat.
- Add a reference to a good 3rd party list of compatible cables, but
provide suggestions for 'known good' vendors.
- Change IP-based USB host-host example to a modern Ethernet one which
works 'out of box' with current Linux systems.
- Explain that USB 3.0 is host-host, even though point-to-point soft
Ethernet can be achieved.
MFC after: 3 weeks