AST-1637 Support model data in BdaBuffer

steps/BdaDdeCal.cc

@@ -294,7 +294,7 @@ bool BdaDdeCal::process(std::unique_ptr<base::BdaBuffer> buffer) {
   predict_timer_.start();
   for (std::shared_ptr<ModelDataStep>& step : steps_) {
     // Feed metadata-only copies of the BDA buffer to the steps.
-    // The steps will create a data buffer in the BDA buffer.
+    // The steps will create and fill the data field in *buffer.
     step->process(
         std::make_unique<BdaBuffer>(*buffer, BdaBuffer::Fields(false)));
   }