tbf/test: Add test for delayed release

This tests checks the implementation of the delayed release of an
downlink TBF.

Ticket: #556
Sponsored-by: On-Waves ehf
diff --git a/tests/tbf/TbfTest.ok b/tests/tbf/TbfTest.ok
index e69de29..13d1458 100644
--- a/tests/tbf/TbfTest.ok
+++ b/tests/tbf/TbfTest.ok
@@ -0,0 +1,2 @@
+=== start test_tbf_delayed_release ===
+=== end test_tbf_delayed_release ===