fix: NTP requests sleep for 1 hour between attempts.

Fixes #74 - When the device is unable to connect to the time servers, it
was looping every two seconds.  This lead to unecessary processing, and
if the device was able to connect to DNS but not the time servers, it
was causing undue load on the DNS server as well.

ntp.go

@@ -20,6 +20,8 @@ func TimeSyncLoop() {
 		err := SyncSystemTime()
 		if err != nil {
 			log.Printf("Failed to sync system time: %v", err)
+			// Sync failed for all 4 endpoints, likely network issue, wait for 1 hour before retrying
+			time.Sleep(1 * time.Hour)
 			continue
 		}
 		log.Printf("Time sync successful, now is: %v, time taken: %v", time.Now(), time.Since(start))