hnbgw: Add SUA client socket towards localhost

This socket doesn't do much yet except to connect to localhost:14001

The host/port needs to be made configurable, and the RUA<->SUA
interfacing needs to be implemented.

Also, we'll need two SUA sockets, one for MSC and one for SGSN.
diff --git a/src/hnbgw.h b/src/hnbgw.h
index 3476c4f..d78dad0 100644
--- a/src/hnbgw.h
+++ b/src/hnbgw.h
@@ -12,6 +12,7 @@
 enum {
 	DMAIN,
 	DHNBAP,
+	DSUA,
 };