mgcp_vty: add user attributes to configuration commands

To make clear which configuration changes (configure terminal)
apply when, add appropriate user attributes to VTY commands.

Change-Id: I2d9487801b3b78f94577264b56d217c926ef76a9
Related: SYS#4937, OS#1601
diff --git a/include/osmocom/mgcp/vty.h b/include/osmocom/mgcp/vty.h
index bf6b7a8..862691f 100644
--- a/include/osmocom/mgcp/vty.h
+++ b/include/osmocom/mgcp/vty.h
@@ -6,3 +6,7 @@
 	MGCP_NODE = _LAST_OSMOVTY_NODE + 1,
 	TRUNK_NODE,
 };
+
+enum mgw_vty_cmd_attr {
+	MGW_CMD_ATTR_NEWCONN = 0,
+};