L2SDP-499, add err message if seconds missed.

src/sdptr.cpp

@@ -87,6 +87,9 @@ void monitor()
             // this means that SD.uptime will reflect the number of seconds
             // this process was actually running, and now - SD.start_time
             // reflects the wall-clock time that passed since start.
+            time_t missed = current_time_timespec.tv_sec - SD.t0.tv_sec;
+            SD.uptime += (uint32_t)missed;
+            cerr << "!!!!!   MONITOR THREAD: Missed " << missed << " seconds   !!!!!" << endl;
             SD.t0.tv_sec = current_time_timespec.tv_sec + SD.timetick;
         }
         SD.t0.tv_nsec = 10000000L;  // 0..999999999 // offset 10ms in a new second