"bias_attr" not used in batch_norm operator in Fluid

[sidgoyal78]

I was adding the documentation for batch norm layer as part of #6526 . It seems that bias_attr is not used in the implementation (even though it is part of the argument list).

Maybe instead of param_attr for the bias, should we use bias_attr?
(https://github.com/PaddlePaddle/Paddle/blob/develop/python/paddle/v2/fluid/layers/nn.py)

[sidgoyal78]

@jacquesqiao : I think bias_attr will be part of **locals(), but can you help me understand what is the use of bias_attr in this operator? (As it doesn't seem to come in the equations, but maybe it comes into the picture somehow?). Thanks.