You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: ip6.go
    path of file: ./repos/sliver/vendor/tailscale.com/net/packet
    
    the code of the file until where you have to start completion: // Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause

package packet

import (
	"encoding/binary"
	"net/netip"

	"tailscale.com/types/ipproto"
)

// ip6HeaderLength is the length of an IPv6 header with no IP options.
const ip6HeaderLength = 40

// IP6Header represents an IPv6 packet header.
type IP6Header struct {
	IPProto ipproto.Proto
	IPID    uint32 // only lower 20 bits used
	Src     netip.Addr
	Dst     netip.Addr
}

// Len implements Header.
func (h IP6Header) Len() int {
	return ip6HeaderLength
}

// Marshal impl
    
func (h IP6Header) Marshal(buf []byte) error {
	if len(buf) < h.Len() {
		return errSmallBuffer
	}
	if len(buf) > maxPacketLength {
		return errLargePacket
	}

	binary.BigEndian.PutUint32(buf[:4], h.IPID&0x000FFFFF)
	buf[0] = 0x60
	binary.BigEndian.PutUint16(buf[4:6], uint16(len(buf)-ip6HeaderLength)) // Total length
	buf[6] = uint8(h.IPProto)                                              // Inner protocol
	buf[7] = 64                                                            // TTL
	src, dst := h.Src.As16(), h.Dst.As16()
	copy(buf[8:24], src[:])
	copy(buf[24:40], dst[:])

	return nil
}