add DSS logging category

Change-Id: Id7e04c9f5088334cd5ec6cfdb6a9b3a2a7e7fda0
diff --git a/include/osmocom/msc/debug.h b/include/osmocom/msc/debug.h
index 28ba482..3347e20 100644
--- a/include/osmocom/msc/debug.h
+++ b/include/osmocom/msc/debug.h
@@ -22,5 +22,6 @@
 	DIUCS,
 	DBSSAP,
 	DSGS,
+	DSS,
 	Debug_LastEntry,
 };