message: Don't clone d6d packet
  Summary: Sending a potentially over-sized d6d packet on PTO might be a bad idea. Plus, a PTO probe containing app data sounds more useful than only "empty" packet.
diff: @@ -757,7 +757,8 @@ SchedulingResult CloningScheduler::scheduleFramesForPacket(
  std::move(builder).releaseOutputBuffer();
  // Look for an outstanding packet that's no larger than the writableBytes
  for (auto& outstandingPacket : conn_.outstandings.packets) {
  - if (outstandingPacket.declaredLost) {
  + if (outstandingPacket.declaredLost ||
  + outstandingPacket.metadata.isD6DProbe) {
  continue;
  }
  auto opPnSpace = outstandingPacket.packet.header.getPacketNumberSpace();
  