【webrtc】接收/发送的rtp包、编解码的VCM包、CopyOnWriteBuffer

• 收到的rtp包RtpPacketReceived 经过RtpDepacketizer 解析后变为ParsedPayload

RtpPacketReceived

• 分配内存，执行memcpy拷贝：然后把 RtpPacketReceived 给到OnRtpPacket 传递：

  uint8_t* media_payload = media_packet.AllocatePayload(rtx_payload.size());
  RTC