W&B DDP fix 2 (#2587)

Revert unintentional change to test batch sizes caused by PR https://github.com/ultralytics/yolov5/pull/2125

train.py

@@ -349,7 +349,7 @@ def train(hyp, opt, device, tb_writer=None):
             if not opt.notest or final_epoch:  # Calculate mAP
                 wandb_logger.current_epoch = epoch + 1
                 results, maps, times = test.test(data_dict,
-                                                 batch_size=total_batch_size,
+                                                 batch_size=batch_size * 2,
                                                  imgsz=imgsz_test,
                                                  model=ema.ema,
                                                  single_cls=opt.single_cls,