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/src/libmsc/Makefile.am b/src/libmsc/Makefile.am
index 72da747..454b970 100644
--- a/src/libmsc/Makefile.am
+++ b/src/libmsc/Makefile.am
@@ -17,6 +17,7 @@
 	$(LIBOSMOMGCPCLIENT_CFLAGS) \
 	$(LIBOSMOGSUPCLIENT_CFLAGS) \
 	$(LIBOSMORANAP_CFLAGS) \
+	$(LIBOSMONETIF_CFLAGS) \
 	$(NULL)
 
 noinst_HEADERS = \
@@ -52,6 +53,9 @@
 	transaction.c \
 	osmo_msc.c \
 	ctrl_commands.c \
+	sgs_iface.c \
+	sgs_server.c \
+	sgs_vty.c \
 	$(NULL)
 if BUILD_IU
 libmsc_a_SOURCES += \