Created by: liym27

This PR : support num_flatten_dims=-1 of static graph API fluid.layers.fc

The corresponding dygraph API Linear doesn't have parameter num_flatten_dims. And the default output of Linear is not equal to fc.

• fc

paddle.fluid.layers.fc(input, size, num_flatten_dims=1, param_attr=None, bias_attr=None, act=None, name=None)

• Linear

class paddle.fluid.dygraph.Linear(input_dim, output_dim, param_attr=None, bias_attr=None, act=None, dtype='float32')

support num_flatten_dims=-1 so that the output of Linear and fc is the same.