NS: Add support for persistent NS-VC configuration

With persistent NS-VC configuration (configured through VTY),
we can respond properly to BSS with a somewhat strange NS
implementation Such as the BSplus.  It enables us to respond
with a proper NS-RESET (including NSVCI/NSEI) when receiving
a NS-ALIVE or other PDU for a BLOCKED/DEAD NS-VC after our
end of the connection is rebooted.
diff --git a/openbsc/include/vty/command.h b/openbsc/include/vty/command.h
index 5f7c819..99fba47 100644
--- a/openbsc/include/vty/command.h
+++ b/openbsc/include/vty/command.h
@@ -109,6 +109,7 @@
 	MGCP_NODE,
 	GBPROXY_NODE,
 	SGSN_NODE,
+	NS_NODE,
 };
 
 /* Node which has some commands and prompt string and configuration