Change the logic in g_socket_listener_add_inet_port() as per the
reasoning in the bug report.

  - If the OS supports neither IPv6 or IPv4, fail.
  - If the OS supports only IPv6, do that.
  - If the OS supports only IPv4, do that.
  - If the OS supports IPv6 and IPv6 "speaks" IPv4 then bind it
    and be done.
  - If the OS supports IPv6 and IPv6 doesn't "speak" IPv4 then
    create an additional socket for IPv4.
  - If binding any socket fails then fail the entire call.

Also, remove the ability to call this function with port == 0.  This
is a useless thing to do anyway since you have no way to know what
port number was actually allocated.  We should have a separate
function to deal with this.