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/wgnetwork/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 =
    
func (m Mode) String() string {
	switch m {
	case XFRM_MODE_TRANSPORT:
		return "transport"
	case XFRM_MODE_TUNNEL:
		return "tunnel"
	case XFRM_MODE_ROUTEOPTIMIZATION:
		return "ro"
	case XFRM_MODE_IN_TRIGGER:
		return "in_trigger"
	case XFRM_MODE_BEET:
		return "beet"
	}
	return fmt.Sprintf("%d", m)
}