test_common: fix compiler warning: include ranap_common.h

  test_common.c:85:2: warning: implicit declaration of function ‘ranap_set_log_area’

Change-Id: Ice192e1f7f1bdafe0941160f43e573349aaceb75
diff --git a/src/tests/test_common.c b/src/tests/test_common.c
index 0af8ceb..eeb0bec 100644
--- a/src/tests/test_common.c
+++ b/src/tests/test_common.c
@@ -37,6 +37,8 @@
 #include <osmocom/core/talloc.h>
 #include <osmocom/core/logging.h>
 
+#include <osmocom/ranap/ranap_common.h>
+
 #include <osmocom/iuh/hnbgw.h>
 
 void *talloc_asn1_ctx;