message: Change tperf pacing timer tick interval to 200us
  Summary:
  In a cross region tperf test this increased bbr throughput from
  <90 MB/s to MB/s
diff: @@ -174,6 +174,7 @@ class TPerfServer {
  settings.defaultCongestionController = congestionControlType;
  if (congestionControlType == quic::CongestionControlType::BBR) {
  settings.pacingEnabled = true;
  + settings.pacingTimerTickInterval = 200us;
  }
  if (gso) {
  settings.batchingMode = QuicBatchingMode::BATCHING_MODE_GSO;
  