[cleanup] Make command nodes static

The cmd_nodes used to configure vty, can mostly be static so
(basic data hiding 101).
diff --git a/ospfd/ospf_dump.c b/ospfd/ospf_dump.c
index 2fcbfe6..de9ef05 100644
--- a/ospfd/ospf_dump.c
+++ b/ospfd/ospf_dump.c
@@ -1509,7 +1509,7 @@
 }
 
 /* Debug node. */
-struct cmd_node debug_node =
+static struct cmd_node debug_node =
 {
   DEBUG_NODE,
   "",