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_test.go

@@ -3,7 +3,6 @@ package flowcontrol
 import (
 	"time"
 
-	"github.com/lucas-clemente/quic-go/internal/congestion"
 	"github.com/lucas-clemente/quic-go/internal/protocol"
 	"github.com/lucas-clemente/quic-go/internal/utils"
 	. "github.com/onsi/ginkgo"
@@ -25,13 +24,13 @@ var _ = Describe("Connection Flow controller", func() {
 	BeforeEach(func() {
 		queuedWindowUpdate = false
 		controller = &connectionFlowController{}
-		controller.rttStats = &congestion.RTTStats{}
+		controller.rttStats = &utils.RTTStats{}
 		controller.logger = utils.DefaultLogger
 		controller.queueWindowUpdate = func() { queuedWindowUpdate = true }
 	})
 
 	Context("Constructor", func() {
-		rttStats := &congestion.RTTStats{}
+		rttStats := &utils.RTTStats{}
 
 		It("sets the send and receive windows", func() {
 			receiveWindow := protocol.ByteCount(2000)