fix(bitswap) shut down async

exchange/bitswap/bitswap.go

@@ -32,12 +32,10 @@ func NetMessageSession(ctx context.Context, p peer.Peer,
 	notif := notifications.New()
 
 	go func() {
-		for {
 		select {
 		case <-ctx.Done():
 			notif.Shutdown()
 		}
-		}
 	}()
 
 	bs := &bitswap{