code: func (b UDP) Encode(u *UDPFields) {
  	binary.BigEndian.PutUint16(b[udpSrcPort:], u.SrcPort)
  	binary.BigEndian.PutUint16(b[udpDstPort:], u.DstPort)
  	binary.BigEndian.PutUint16(b[udpLength:], u.Length)
  	binary.BigEndian.PutUint16(b[udpChecksum:], u.Checksum)
  }
docs: // Encode encodes all the fields of the udp header.