func (b IPv4Header) Len() int {
	return int(b[0]&0x0f) << 2
}
Len is header length
package camo
import (
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"net"
)
const (
	IPv4HeaderLen = 20
	IPv6HeaderLen = 40
)
func GetIPPacketVersion(b []byte) int {
	return int(b[0] >> 4)
}
type IPv4Header []byte
func (b IPv4Header) Version() int {
	return int(b[0] >> 4)
}