vty: reserve nodes for libosmo-abis

This patch reserves E1INP_NODE and IPA_NODE for libosmo-abis
VTY interfaces.
diff --git a/include/osmocom/vty/command.h b/include/osmocom/vty/command.h
index 08819d1..4104d76 100644
--- a/include/osmocom/vty/command.h
+++ b/include/osmocom/vty/command.h
@@ -74,6 +74,9 @@
 
 	VTY_NODE,		/* Vty node. */
 
+	E1INP_NODE,		/* E1 line in libosmo-abis. */
+	IPA_NODE,		/* IPA proxying commands in libosmo-abis. */
+
 	_LAST_OSMOVTY_NODE
 };