nitb: Make the last change configurable

Introduce a NITB node and add the subscriber creation as
config name in there.
diff --git a/openbsc/include/openbsc/vty.h b/openbsc/include/openbsc/vty.h
index 9e07eb7..818a20e 100644
--- a/openbsc/include/openbsc/vty.h
+++ b/openbsc/include/openbsc/vty.h
@@ -32,6 +32,7 @@
 	TRUNK_NODE,
 	PGROUP_NODE,
 	MNCC_INT_NODE,
+	NITB_NODE,
 	BSC_NODE,
 	SMPP_NODE,
 	SMPP_ESME_NODE,