Ensure that unsupported SetFeature/ClearFeature request targets cause a STALL back to the host.

LUFA/Drivers/USB/LowLevel/Pipe.c

@@ -199,6 +199,9 @@ uint8_t Pipe_Discard_Stream(uint16_t Length
 	return PIPE_RWSTREAM_NoError;
 }
 
+/* The following abuses the C preprocessor in order to copy-past common code with slight alterations,
+ * so that the code needs to be written once. It is a crude form of templating to reduce code maintenance. */
+
 #define  TEMPLATE_FUNC_NAME                        Pipe_Write_Stream_LE
 #define  TEMPLATE_BUFFER_TYPE                      const void*
 #define  TEMPLATE_TOKEN                            PIPE_TOKEN_OUT