Add test case that is not registering the timer again

yesterday's crash with the llist_del instead of using del_timer
was due this kind of bug. Add a test case.
diff --git a/tests/timer/timer_test.c b/tests/timer/timer_test.c
index 4d98aef..3f5828b 100644
--- a/tests/timer/timer_test.c
+++ b/tests/timer/timer_test.c
@@ -35,6 +35,11 @@
     .data = (void*)2,
 };
 
+static struct timer_list timer_three = {
+    .cb = timer_fired,
+    .data = (void*)3,
+};
+
 static void timer_fired(unsigned long data)
 {
     printf("Fired timer: %lu\n", data);
@@ -44,6 +49,8 @@
         del_timer(&timer_two);
     } else if (data == 2) {
         printf("Should not be fired... bug in del_timer\n");
+    } else if (data == 3) {
+        printf("Timer fired not registering again\n");
     } else  {
         printf("wtf... wrong data\n");
     }
@@ -55,6 +62,7 @@
 
     schedule_timer(&timer_one, 3, 0);
     schedule_timer(&timer_two, 5, 0);
+    schedule_timer(&timer_three, 4, 0);
 
     while (1) {
         bsc_select_main();