func NewEchoRequest(msg icmp.Message, dest net.IP, wg *sync.WaitGroup) *EchoRequest {
	return &EchoRequest{
		Message:     msg,
		Destination: dest,
		WaitGroup:   wg,
		ID:          packetKey(dest.String(), msg.Body.(*icmp.Echo).ID, msg.Body.(*icmp.Echo).Seq),
	}
}
create a new EchoRequest instance.
package pinger
import (
	"fmt"
	"net"
	"sync"
	"time"
	"golang.org/x/net/icmp"
)
type EchoRequest struct {
	icmp.Message
	Destination net.IP
	Sent        time.Time
	Received    time.Time
	ID          string
	WaitGroup   *sync.WaitGroup
}