tests/hnb-test-ranap: Fix missing include for ranap_bcd_decode

Change-Id: If8b799777598377048512c338f6384560b445ba3
diff --git a/src/tests/hnb-test-ranap.c b/src/tests/hnb-test-ranap.c
index 3db876c..629726b 100644
--- a/src/tests/hnb-test-ranap.c
+++ b/src/tests/hnb-test-ranap.c
@@ -1,5 +1,6 @@
 #include <osmocom/core/msgb.h>
 #include <osmocom/ranap/ranap_ies_defs.h>
+#include <osmocom/ranap/iu_helpers.h>
 
 #include "hnb-test-layers.h"