model diff acc kernel (#197)

* refine copy actors and model diff acc actor

* use set_num_of_not_eord

* fix element cnt

oneflow/core/kernel/model_diff_accumulate_kernel.cpp

@@ -9,8 +9,7 @@ void MdDiffAccKernel<device_type, FloatingPointType>::Forward(
   Blob* in_blob = BnInOp2BlobPtr("model_diff");
   Blob* out_blob = BnInOp2BlobPtr("model_diff_acc");
   KernelUtil<device_type, FloatingPointType>::BlasAxpy(
-      ctx, in_blob->shape().elem_cnt() * sizeof(FloatingPointType),
-      static_cast<FloatingPointType>(1.0),
+      ctx, in_blob->shape().elem_cnt(), static_cast<FloatingPointType>(1.0),
       static_cast<const FloatingPointType*>(in_blob->dptr()), 1,
       static_cast<FloatingPointType*>(out_blob->mut_dptr()), 1);
 }