remove check for CONGESTION_FEEDBACK in the packet unpacker

CONGESTION_FEEDBACK was reserved for future use in gQUIC, but has never
actually been implemented. It won't make it to IETF QUIC, so we don't
need to check for it. Note that we'd still reject a CONGESTION_FEEDBACK
frame, since we're rejecting any unknown frame type.

packet_unpacker.go

@@ -2,7 +2,6 @@ package quic
 
 import (
 	"bytes"
-	"errors"
 	"fmt"
 
 	"github.com/lucas-clemente/quic-go/internal/protocol"
@@ -64,8 +63,6 @@ func (u *packetUnpacker) Unpack(headerBinary []byte, hdr *wire.Header, data []by
 			if err != nil {
 				err = qerr.Error(qerr.InvalidAckData, err.Error())
 			}
-		} else if typeByte&0xe0 == 0x20 {
-			err = errors.New("unimplemented: CONGESTION_FEEDBACK")
 		} else {
 			switch typeByte {
 			case 0x01:

packet_unpacker_test.go

@@ -92,12 +92,6 @@ var _ = Describe("Packet unpacker", func() {
 		Expect(readFrame.LargestAcked).To(Equal(protocol.PacketNumber(0x13)))
 	})
 
-	It("errors on CONGESTION_FEEDBACK frames", func() {
-		setData([]byte{0x20})
-		_, err := unpacker.Unpack(hdrBin, hdr, data)
-		Expect(err).To(MatchError("unimplemented: CONGESTION_FEEDBACK"))
-	})
-
 	It("handles PADDING frames", func() {
 		setData([]byte{0, 0, 0}) // 3 bytes PADDING
 		packet, err := unpacker.Unpack(hdrBin, hdr, data)