message: Simplify RTT update calculation
  No need for two lots of division
diff: @@ -70,8 +70,8 @@ impl RttVals {
  self.latest_rtt - smoothed_rtt
  };
  - self.rttvar = (self.rttvar * 3 / 4) + (rttvar_sample / 4);
  - self.smoothed_rtt = Some((smoothed_rtt * 7 / 8) + (self.latest_rtt / 8));
  + self.rttvar = (self.rttvar * 3 + rttvar_sample) / 4;
  + self.smoothed_rtt = Some((smoothed_rtt * 7 + self.latest_rtt) / 8);
  }
  }
  }
  