Added method to retrieve time to next time critical job

src/lmic/oslmic.c

@@ -167,3 +167,10 @@ bit_t os_queryTimeCriticalJobs(ostime_t time) {
     else
         return 0;
 }
+
+ostime_t os_timeToNextTimeCriticalJob() {
+    if (OS.runnablejobs) return 0;
+
+	if (!OS.scheduledjobs) return 0x7FFFFFFFl;//ostime_t_max;
+	return OS.scheduledjobs->deadline - os_getTime();
+}

src/lmic/oslmic.h

@@ -216,6 +216,10 @@ u1_t os_getBattLevel (void);
 //! Return non-zero if any jobs are scheduled between now and now+time.
 bit_t os_queryTimeCriticalJobs(ostime_t time);
 #endif
+#ifndef os_timeToNextTimeCriticalJob
+// return the time to the next scheduled job, or ostime_t_max if no job is scheduled
+ostime_t os_timeToNextTimeCriticalJob();
+#endif
 
 #ifndef os_rlsbf4
 //! Read 32-bit quantity from given pointer in little endian byte order.