Plane: set system time on GPS lock

ArduPlane/ArduPlane.pde

@@ -1027,6 +1027,9 @@ static void update_GPS(void)
             } else {
                 init_home();
 
+                // set system clock for log timestamps
+                hal.util->set_system_clock(g_gps->time_epoch_usec());
+
                 if (g.compass_enabled) {
                     // Set compass declination automatically
                     compass.set_initial_location(g_gps->latitude, g_gps->longitude);