Convert MXNet layer to ONNX

def convert_layer(node, **kwargs):
        """Convert MXNet layer to ONNX"""
        op = str(node["op"])
        if op not in MXNetGraph.registry_:
            raise AttributeError("No conversion function registered for op type %s yet." % op)
        convert_func = MXNetGraph.registry_[op]
        return convert_func(node, **kwargs)