[NETDEV_SET_QUEUE_CPU_AFFINITY] Improve error checking from snprintf

src/netdev_set_queue_cpu_affinity.c

@@ -31,7 +31,7 @@ int main(int argc, char *argv[])
 	else
 		ret = snprintf(fname, len, "/sys/class/net/%s/queues/%s/rps_cpus",
 			       dev, irq_queue);
-	if ((ret < 0) || (ret == len))
+	if ((ret < 0) || (ret >= len))
 		exit(3);
 
 	fd = open(fname, O_WRONLY);