[cleanup] Make command nodes static

The cmd_nodes used to configure vty, can mostly be static so
(basic data hiding 101).
diff --git a/lib/smux.c b/lib/smux.c
index fd0c89c..349cc2f 100644
--- a/lib/smux.c
+++ b/lib/smux.c
@@ -73,7 +73,7 @@
 int fail = 0;
 
 /* SMUX node. */
-struct cmd_node smux_node =
+static struct cmd_node smux_node =
 {
   SMUX_NODE,
   ""                            /* SMUX has no interface. */