implement a timer_list check before we return into the select() loop

this helps us to debug timer_list corruption
diff --git a/openbsc/src/timer.c b/openbsc/src/timer.c
index a942ffd..6f974a2 100644
--- a/openbsc/src/timer.c
+++ b/openbsc/src/timer.c
@@ -172,3 +172,14 @@
 
 	return work;
 }
+
+int bsc_timer_check(void)
+{
+	struct timer_list *timer;
+	int i;
+
+	llist_for_each_entry(timer, &timer_list, entry) {
+		i++;
+	}
+	return i;
+}