Add SGs Interface

Add an SGs interface (3GPP TS 29.118) to osmo-msc in order to support
SMS tunneling and Circuit Switched Fallback (CSFB)

Change-Id: I73359925fc1ca72b33a1466e6ac41307f2f0b11d
Related: OS#3615
diff --git a/tests/msc_vlr/msc_vlr_test_ss.c b/tests/msc_vlr/msc_vlr_test_ss.c
index 0390196..b264d07 100644
--- a/tests/msc_vlr/msc_vlr_test_ss.c
+++ b/tests/msc_vlr/msc_vlr_test_ss.c
@@ -21,6 +21,7 @@
  */
 
 #include "msc_vlr_tests.h"
+#include "stubs.h"
 
 #define IMSI "901700000004620"