RTCP Reception mechanism

Add a channel to the RTCTrack object to
recieve incoming RTCP packets with.
Relates to #119

pkg/rtcp/packet.go

@@ -5,3 +5,78 @@ type Packet interface {
 	Marshal() ([]byte, error)
 	Unmarshal(rawPacket []byte) error
 }
+
+type PacketWithHeader struct {
+ 	Header
+	Packet
+	RawPacket []byte
+}
+
+func (p PacketWithHeader) Marshal() ([]byte, error) {
+	return p.Packet.Marshal()
+}
+
+func (p *PacketWithHeader) Unmarshal(rawPacket []byte) error {
+
+	p.RawPacket = rawPacket
+	
+	if err := p.Header.Unmarshal(rawPacket); err != nil {
+		return err
+	}
+
+	switch p.Header.Type {
+	case TypeSenderReport:
+		sr := new(SenderReport)
+		err := sr.Unmarshal(rawPacket)
+		if (err == nil) {
+			p.Packet = sr
+		} else {
+			return err
+		}
+	case TypeReceiverReport:
+		rr := new(ReceiverReport)
+		err := rr.Unmarshal(rawPacket)
+		if (err == nil) {
+			p.Packet = rr
+		} else {
+			return err
+		}
+	case TypeSourceDescription:
+		sdes := new(SourceDescription)
+		err := sdes.Unmarshal(rawPacket)
+		if (err == nil) {
+			p.Packet = sdes
+		} else {
+			return err
+		}
+	case TypeGoodbye:
+		bye := new(Goodbye)
+		err := bye.Unmarshal(rawPacket)
+		if (err == nil) {
+			p.Packet = bye
+		} else {
+			return err
+		}
+	case TypeTransportSpecificFeedback:
+		rrr := new(RapidResynchronizationRequest)
+		err := rrr.Unmarshal(rawPacket)
+		if (err == nil) {
+			p.Packet = rrr
+		} else {
+			return err
+		}
+	case TypePayloadSpecificFeedback:
+		psfb := new(PictureLossIndication)
+		err := psfb.Unmarshal(rawPacket)
+		if (err == nil) {
+			p.Packet = psfb
+		} else {
+			return err
+		}
+	default:
+		return errWrongType
+	}
+
+	
+	return nil
+}