libmsc: properly name the MSC_CONN_USE token for SS

Previously the MSC_CONN_USE token for Supplementary Services was
called 'MSC_CONN_USE_TRANS_USSD'. Non-call related Supplementary
Services is not only about USSD, so let's rename it.

Change-Id: I5b3517c87a32fa64dea6b0c912f2b76c5c25a112
diff --git a/include/osmocom/msc/osmo_msc.h b/include/osmocom/msc/osmo_msc.h
index 632b231..995b195 100644
--- a/include/osmocom/msc/osmo_msc.h
+++ b/include/osmocom/msc/osmo_msc.h
@@ -91,7 +91,7 @@
 	MSC_CONN_USE_CM_SERVICE,
 	MSC_CONN_USE_TRANS_CC,
 	MSC_CONN_USE_TRANS_SMS,
-	MSC_CONN_USE_TRANS_USSD,
+	MSC_CONN_USE_TRANS_NC_SS,
 	MSC_CONN_USE_SILENT_CALL,
 	MSC_CONN_USE_RELEASE,
 };