switch handover penalty timers to CLOCK_MONOTONIC

To be able to add a fake time to handover tests, the penalty timers need
to use an osmo_* time source.

There already is a fixme comment rightfully asking for a monotonic
clock, so this change is overdue anyway.

An upcoming patch will prove that this works:
"handover tests: test passing of penalty timeout"
I65e59cc7309778cf9d71612669ce84d101c8135e

Related: SYS#5198
Change-Id: Ifb1ab3165db50511aed4f65aa445798367d7e19e

src/osmo-bsc/penalty_timers.c

@@ -30,10 +30,10 @@
 
 static unsigned int time_now(void)
 {
-	time_t now;
-	time(&now);
-	/* FIXME: use monotonic clock */
-	return (unsigned int)now;
+	struct timespec tp;
+	if (osmo_clock_gettime(CLOCK_MONOTONIC, &tp))
+		return 0;
+	return (unsigned int)tp.tv_sec;
 }
 
 /* Add a penalty timer for a target cell ID.