Always call update_use_power() instead of directly setting the use_power var.

- This will let us react to the change appropriately.
- While we're here, lets define some constants so we can stop using bare numbers.
- Always use those constants when calling update_use_power()

code/modules/power/antimatter/control.dm

@@ -211,10 +211,10 @@
 /obj/machinery/power/am_control_unit/proc/toggle_power()
 	active = !active
 	if(active)
-		use_power = 2
+		update_use_power(USE_POWER_ACTIVE)
 		visible_message("The [src.name] starts up.")
 	else
-		use_power = 1
+		update_use_power(USE_POWER_IDLE)
 		visible_message("The [src.name] shuts down.")
 	update_icon()
 	return