Previously, we had stubs for setsockopt with SO_BROADCAST for tcp and udp:

(libc::SOL_SOCKET, libc::SO_BROADCAST) => {
    // TODO: implement this, pkg.go.dev/net uses it
    log::trace!("setsockopt SO_BROADCAST not yet implemented");
}

The old behaviour for tcp/udp was:

• getsockopt:
  • return ENOPROTOOPT
• setsockopt:
  • show trace (for tcp) or "warn_once_then_debug" (for udp) log and return 0

The new behaviour for tcp/udp is:

• getsockopt:
  • always returns 0 since we don't support broadcast sockets
• setsockopt:
  • if value is 0, do nothing and return 0
  • if value is not 0, show "warn_once_then_debug" log and return 0

Our tests aren't set up to test get/setsockopt for unix sockets, so I didn't implement the option for unix sockets. I would expect it to return an error.

Closes #3439.