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: xfrm.go
    path of file: ./repos/docker-ce/components/engine/vendor/github.com/vishvananda/netlink
    
    the code of the file until where you have to start completion: package netlink

import (
	"fmt"

	"golang.org/x/sys/unix"
)

// Proto is an enum representing an ipsec protocol.
type Proto uint8

const (
	XFRM_PROTO_ROUTE2    Proto = unix.IPPROTO_ROUTING
	XFRM_PROTO_ESP       Proto =
    
func (p Proto) String() string {
	switch p {
	case XFRM_PROTO_ROUTE2:
		return "route2"
	case XFRM_PROTO_ESP:
		return "esp"
	case XFRM_PROTO_AH:
		return "ah"
	case XFRM_PROTO_HAO:
		return "hao"
	case XFRM_PROTO_COMP:
		return "comp"
	case XFRM_PROTO_IPSEC_ANY:
		return "ipsec-any"
	}
	return fmt.Sprintf("%d", p)
}