config: avoid switching between sleep and active state too often

Unfortunately, the offset voltage of the opamp for charge current
measurement breaks measurement at low currents with a small shunt, so at
dusk, when currents become low, it may happen that 0 current is measured
while the battery is still being charged. This would falsely trigger the
transition to sleep state. To improve this situation, we simply keep the
charger active for a longer time.

src/config.h

@@ -30,7 +30,7 @@
 #define SLEEP_SOLAR_CURRENT    1
 
 /* Delay between state change and sleep state check (in ms). */
-#define SLEEP_STATE_DELAY      100
+#define SLEEP_STATE_DELAY    60000
 
 /* Delay between charging switch state change and sleep state check(in ms). */
 #define SLEEP_SWITCH_DELAY    1000