send a StopWaiting with every ACK in QUIC 34

fixes #185

ackhandlerlegacy/interfaces.go

@@ -12,6 +12,8 @@ type SentPacketHandler interface {
 	SentPacket(packet *Packet) error
 	ReceivedAck(ackFrame *frames.AckFrame, withPacketNumber protocol.PacketNumber) error
 
+	GetStopWaitingFrame() *frames.StopWaitingFrame
+
 	ProbablyHasPacketForRetransmission() bool
 	DequeuePacketForRetransmission() (packet *Packet)
 

ackhandlerlegacy/sent_packet_handler.go

@@ -312,6 +312,10 @@ func (h *sentPacketHandler) GetLargestAcked() protocol.PacketNumber {
 	return h.LargestObserved
 }
 
+func (h *sentPacketHandler) GetStopWaitingFrame() *frames.StopWaitingFrame {
+	panic("Legacy AckHandler should use StopWaitingManager")
+}
+
 func (h *sentPacketHandler) CongestionAllowsSending() bool {
 	return h.BytesInFlight() <= h.congestion.GetCongestionWindow()
 }