Revert "p2p/simulations/examples: use atomic.Int64 (ethereum#27861)"

This reverts commit 7b3e2ee.

p2p/simulations/examples/ping-pong.go

@@ -91,7 +91,7 @@ func main() {
 type pingPongService struct {
 	id       enode.ID
 	log      log.Logger
-	received atomic.Int64
+	received int64
 }
 
 func newPingPongService(id enode.ID) *pingPongService {
@@ -125,7 +125,7 @@ func (p *pingPongService) Info() interface{} {
 	return struct {
 		Received int64 `json:"received"`
 	}{
-		p.received.Load(),
+		atomic.LoadInt64(&p.received),
 	}
 }
 
@@ -162,7 +162,7 @@ func (p *pingPongService) Run(peer *p2p.Peer, rw p2p.MsgReadWriter) error {
 				return
 			}
 			log.Info("received message", "msg.code", msg.Code, "msg.payload", string(payload))
-			p.received.Add(1)
+			atomic.AddInt64(&p.received, 1)
 			if msg.Code == pingMsgCode {
 				log.Info("sending pong")
 				go p2p.Send(rw, pongMsgCode, "PONG")