Add typedef extra_fan_t

Marlin/src/lcd/menu/menu_item.h

   #define _FAN_EDIT_ITEMS(F,L) do{ \
     editable.uint8 = thermalManager.fan_speed[F]; \
     EDIT_ITEM_FAST_N(percent, F, MSG_##L, &editable.uint8, 0, 255, on_fan_update); \
-    EDIT_EXTRA_FAN_SPEED(percent, F, MSG_EXTRA_##L, &thermalManager.new_fan_speed[F], 3, 255); \
+    EDIT_EXTRA_FAN_SPEED(percent, F, MSG_EXTRA_##L, &thermalManager.extra_fan_speed[F].speed, 3, 255); \
   }while(0)
 
   #if FAN_COUNT > 1

Marlin/src/module/temperature.cpp

   uint8_t Temperature::fan_speed[FAN_COUNT]; // = { 0 }
 
   #if ENABLED(EXTRA_FAN_SPEED)
-    uint8_t Temperature::old_fan_speed[FAN_COUNT], Temperature::new_fan_speed[FAN_COUNT];
 
-    void Temperature::set_temp_fan_speed(const uint8_t fan, const uint16_t tmp_temp) {
-      switch (tmp_temp) {
+    Temperature::extra_fan_t Temperature::extra_fan_speed[FAN_COUNT];
+
+    /**
+     * Handle the M106 P<fan> T<speed> command:
+     *  T1       = Restore fan speed saved on the last T2
+     *  T2       = Save the fan speed, then set to the last T<3-255> value
+     *  T<3-255> = Set the "extra fan speed"
+     */
+    void Temperature::set_temp_fan_speed(const uint8_t fan, const uint16_t command_or_speed) {
+      switch (command_or_speed) {
         case 1:
-          set_fan_speed(fan, old_fan_speed[fan]);
+          set_fan_speed(fan, extra_fan_speed[fan].saved);
           break;
         case 2:
-          old_fan_speed[fan] = fan_speed[fan];
-          set_fan_speed(fan, new_fan_speed[fan]);
+          extra_fan_speed[fan].saved = fan_speed[fan];
+          set_fan_speed(fan, extra_fan_speed[fan].speed);
           break;
         default:
-          new_fan_speed[fan] = _MIN(tmp_temp, 255U);
+          extra_fan_speed[fan].speed = _MIN(command_or_speed, 255U);
           break;
       }
     }

Marlin/src/module/temperature.h

       }
 
       #if ENABLED(EXTRA_FAN_SPEED)
-        static uint8_t old_fan_speed[FAN_COUNT], new_fan_speed[FAN_COUNT];
-        static void set_temp_fan_speed(const uint8_t fan, const uint16_t tmp_temp);
+        typedef struct { uint8_t saved, speed; } extra_fan_t;
+        static extra_fan_t extra_fan_speed[FAN_COUNT];
+        static void set_temp_fan_speed(const uint8_t fan, const uint16_t command_or_speed);
       #endif
 
       #if EITHER(PROBING_FANS_OFF, ADVANCED_PAUSE_FANS_PAUSE)