[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/filter.c b/lib/filter.c
index 7aeb8de..af8d587 100644
--- a/lib/filter.c
+++ b/lib/filter.c
@@ -1857,7 +1857,7 @@
 }
 
 /* Access-list node. */
-struct cmd_node access_node =
+static struct cmd_node access_node =
 {
   ACCESS_NODE,
   "",				/* Access list has no interface. */
@@ -1953,7 +1953,7 @@
 }
 
 #ifdef HAVE_IPV6
-struct cmd_node access_ipv6_node =
+static struct cmd_node access_ipv6_node =
 {
   ACCESS_IPV6_NODE,
   "",