message: show mode in configuration format
diff: @@ -170,7 +170,7 @@ impl Tun {
  assert!(mtu > 0 && mtu as usize > IFF_PI_PREFIX_LEN);
  info!(
  - "shadowsocks tun device {}, address {}, netmask {}, mtu {}, mode {:?}",
  + "shadowsocks tun device {}, address {}, netmask {}, mtu {}, mode {}",
  self.device.get_ref().name(),
  self.device.get_ref().address().expect("address"),
  self.device.get_ref().netmask().expect("netmask"),
  