open depthwise_conv2d in dygraph (#22373)

test=develop

python/paddle/fluid/dygraph/nn.py

@@ -183,14 +183,11 @@ class Conv2D(layers.Layer):
         self._bias_attr = bias_attr
         self._dtype = dtype
 
-        # TODO: recover the usage of depthwise_conv2d when it's
-        #  kernel fixed https://github.com/PaddlePaddle/Paddle/issues/17098
-        # if (self._num_channels == self._groups and
-        #         num_filters % self._num_channels == 0 and not self._use_cudnn):
-        #     self._l_type = 'depthwise_conv2d'
-        # else:
-        #     self._l_type = 'conv2d'
-        self._l_type = 'conv2d'
+        if (self._num_channels == self._groups and
+                num_filters % self._num_channels == 0 and not self._use_cudnn):
+            self._l_type = 'depthwise_conv2d'
+        else:
+            self._l_type = 'conv2d'
 
         self._num_channels = num_channels
         if self._groups is None:
@@ -234,7 +231,7 @@ class Conv2D(layers.Layer):
             'use_mkldnn': False,
         }
 
-        if in_dygraph_mode():
+        if in_dygraph_mode() and self._l_type == 'conv2d':
             outs = core.ops.conv2d(inputs, attrs)
             pre_bias = outs['Output'][0]