message: Do not disable PTO when packets outstanding == 0 for initial/handshake
  See recovery 6.2.2.1, the client needs to keep sending packets until it
  receives HandshakeDone, even if all previous PTOs are acked and
  in_flight_outstanding drops to zero.
diff: @@ -313,11 +313,16 @@ impl LossRecoverySpace {
  debug_assert!(self.in_flight_outstanding > 0);
  self.in_flight_outstanding -= 1;
  if self.in_flight_outstanding == 0 {
  - qtrace!("remove_packet outstanding == 0");
  + qtrace!("remove_packet outstanding == 0 for space {}", self.space);
  +
  + // See above comments; keep PTO armed for Initial/Handshake even
  + // if no outstanding packets.
  + if self.space == PNSpace::ApplicationData {
  self.pto_base_time = None;
  }
  }
  }
  + }
  // Remove all the acked packets. Returns them in ascending order -- largest
  // (i.e. highest PN) acked packet is last.
  