Merge pull request #5696 from thinkyhead/rc_volumetric_default

Allow enabling volumetric filament on config load

Marlin/Marlin_main.cpp

@@ -388,7 +388,13 @@ int feedrate_percentage = 100, saved_feedrate_percentage,
     flow_percentage[EXTRUDERS] = ARRAY_BY_EXTRUDERS1(100);
 
 bool axis_relative_modes[] = AXIS_RELATIVE_MODES,
-     volumetric_enabled = false;
+     volumetric_enabled = 
+      #if ENABLED(VOLUMETRIC_DEFAULT_ON)
+        true
+      #else
+        false
+      #endif
+      ;
 float filament_size[EXTRUDERS] = ARRAY_BY_EXTRUDERS1(DEFAULT_NOMINAL_FILAMENT_DIA),
       volumetric_multiplier[EXTRUDERS] = ARRAY_BY_EXTRUDERS1(1.0);