code: public byte[] toBytes() {
          byte[] data = new byte[4];
          data[0] = (byte) (packetBodyLength & 0xFF);
          data[1] = (byte) (packetBodyLength >>> 8);
          data[2] = (byte) (packetBodyLength >>> 16);
          data[3] = getPacketSequenceNumber();
          return data;
      }
docs: little-endian byte order