move the RTTStats to the utils package

The RTTStats are used by the logging package. In order to instrument the
congestion package, the RTTStats can't be part of that package any more
(to avoid an import loop).

internal/flowcontrol/connection_flow_controller.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"time"
 
-	"github.com/lucas-clemente/quic-go/internal/congestion"
 	"github.com/lucas-clemente/quic-go/internal/protocol"
 	"github.com/lucas-clemente/quic-go/internal/qerr"
 	"github.com/lucas-clemente/quic-go/internal/utils"
@@ -24,7 +23,7 @@ func NewConnectionFlowController(
 	receiveWindow protocol.ByteCount,
 	maxReceiveWindow protocol.ByteCount,
 	queueWindowUpdate func(),
-	rttStats *congestion.RTTStats,
+	rttStats *utils.RTTStats,
 	logger utils.Logger,
 ) ConnectionFlowController {
 	return &connectionFlowController{