Prevent poll() in select.c to timeout too early

Adjust osmo_timers_nearest_ms() to round up the remaining time.

Note that poll() has a granularity of 1 millisecond.

Previously, when rounding down the remaining time, osmo_select_main()
would return too early, before the nearest timer timed out.
Consequently, the main loop repeatedly called osmo_select_main() until
the timer actually timed out, resulting in excessive CPU usage.
By modifying osmo_timers_nearest_ms() to round up the remaining time,
we ensure accurate timeout calculations, preventing unnecessary CPU
consumption during the main loop.

The patch only applies to non-embedded version of libosmocore, because
the impact on embedded systems is not verified tested.

Related: OS#6339
Change-Id: I79de77c79af4d50d1eb9ca0c5417123ff760dca3

src/core/timer.c

@@ -191,7 +191,16 @@ int osmo_timers_nearest_ms(void)
 		return -1;
 
 	nearest_ms = nearest_p->tv_sec * 1000;
+#ifndef EMBEDDED
+	/* By adding 999 milliseconds, we ensure rounding up to the nearest
+	 * whole millisecond. This approach prevents the return of 0 when the
+	 * timer is still active, and it guarantees that the calling process
+	 * does not wait for a duration shorter than the time remaining on the
+	 * timer. */
+	nearest_ms += (nearest_p->tv_usec + 999) / 1000;
+#else
 	nearest_ms += nearest_p->tv_usec / 1000;
+#endif
 
 	return nearest_ms;
 }