added RTC timesync during startup

include/rtc.h

@@ -5,9 +5,17 @@
 #include <Wire.h> // must be included here so that Arduino library object file references work
 #include <RtcDS3231.h>
 
+typedef enum {
+  useless = 0,     // waiting for good enough signal
+  dirty = 1,       // time data available but inconfident
+  reserve = 2,     // clock was once synced but now may deviate
+  synced_LORA = 3, // clock driven by LORAWAN network
+  synced_GPS = 4   // best possible quality, clock is driven by GPS
+} clock_state_t;
+
 int rtc_init(void);
-int set_rtc(uint32_t UTCTime);
-int set_rtc(RtcDateTime now);
+int set_rtc(uint32_t UTCTime, clock_state_t state);
+int set_rtc(RtcDateTime now, clock_state_t state);
 uint32_t get_rtc();
 float get_rtc_temp();