use a single bytes.Reader for frame parsing (#3536)

internal/wire/interface.go

@@ -1,8 +1,6 @@
 package wire
 
 import (
-	"bytes"
-
 	"github.com/lucas-clemente/quic-go/internal/protocol"
 )
 
@@ -14,6 +12,6 @@ type Frame interface {
 
 // A FrameParser parses QUIC frames, one by one.
 type FrameParser interface {
-	ParseNext(*bytes.Reader, protocol.EncryptionLevel) (Frame, error)
+	ParseNext([]byte, protocol.EncryptionLevel) (int, Frame, error)
 	SetAckDelayExponent(uint8)
 }