more robust usage of osmo_timer API for osmo-hlr luop timer

Use osmo_timer_setup() to set up the luop timer, instead of
settting the timer up manually.

Delete the timer before the luop is freed to prevent a potential
crash in case the timer is already armed and the function call
chain leading up to lu_op_free() does not cancel the timer.

Found while studying code to prepare work on issue OS#2785.

This change has been tested with 'make check' and TTCN3 HLR tests.

Related: OS#2785
Change-Id: I1a7596675b2d94217895f0f3d3f67b86ef123c2e
diff --git a/src/luop.c b/src/luop.c
index 4ef4ea3..02c41d0 100644
--- a/src/luop.c
+++ b/src/luop.c
@@ -108,8 +108,7 @@
 	luop = talloc_zero(srv, struct lu_operation);
 	OSMO_ASSERT(luop);
 	luop->gsup_server = srv;
-	luop->timer.cb = lu_op_timer_cb;
-	luop->timer.data = luop;
+	osmo_timer_setup(&luop->timer, lu_op_timer_cb, luop);
 
 	return luop;
 }
@@ -119,6 +118,10 @@
 	/* Only attempt to remove when it was ever added to a list. */
 	if (luop->list.next)
 		llist_del(&luop->list);
+
+	/* Delete timer just in case it is still pending. */
+	osmo_timer_del(&luop->timer);
+
 	talloc_free(luop);
 }