Change the type of conv2d in Python API.

Author: qingqing01

python/paddle/v2/fluid/layers.py

@@ -764,7 +764,7 @@ def _get_default_param_initializer():
     pre_bias = helper.create_tmp_variable(dtype)
 
     helper.append_op(
-        type='conv2d',
+        type='conv2d_cudnn',
         inputs={
             'Input': input,
             'Filter': filter,