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/include/osmocom/msc/vty.h b/include/osmocom/msc/vty.h
index 6a55df7..2a3b18b 100644
--- a/include/osmocom/msc/vty.h
+++ b/include/osmocom/msc/vty.h
@@ -23,6 +23,7 @@
 	SMPP_NODE,
 	SMPP_ESME_NODE,
 	HLR_NODE,
+	CFG_SGS_NODE,
 };
 
 int bsc_vty_init_extra(void);