code: func (b IPv6) Encode(i *IPv6Fields) {
  	b.SetTOS(i.TrafficClass, i.FlowLabel)
  	b.SetPayloadLength(i.PayloadLength)
  	b[nextHdr] = i.NextHeader
  	b[hopLimit] = i.HopLimit
  	copy(b[v6SrcAddr:v6SrcAddr+IPv6AddressSize], i.SrcAddr)
  	copy(b[v6DstAddr:v6DstAddr+IPv6AddressSize], i.DstAddr)
  }
docs: // Encode encodes all the fields of the ipv6 header.