code: func IPv4FragmentHash(h header.IPv4) uint32 {
  	x := uint32(h.ID())<<16 | uint32(h.Protocol())
  	t := h.SourceAddress()
  	y := uint32(t[0]) | uint32(t[1])<<8 | uint32(t[2])<<16 | uint32(t[3])<<24
  	t = h.DestinationAddress()
  	z := uint32(t[0]) | uint32(t[1])<<8 | uint32(t[2])<<16 | uint32(t[3])<<24
  	return Hash3Words(x, y, z, hashIV)
  }
docs: // IPv4FragmentHash computes the hash of the IPv4 fragment as suggested in RFC 791.