vty: Move the assumption of the config nodes into a function

Move the assumption that something is a child of the CONFIG_NODE
into a new function. The next step will be to use something else
for that.
diff --git a/src/vty/command.c b/src/vty/command.c
index 598e63c..bec28a0 100644
--- a/src/vty/command.c
+++ b/src/vty/command.c
@@ -139,6 +139,12 @@
 	return strcmp(a->cmd, b->cmd);
 }
 
+static int is_config(struct vty *vty)
+{
+	/* Assume that everything above CONFIG_NODE is a config node */
+	return vty->node > CONFIG_NODE;
+}
+
 /* Sort each node's command element according to command string. */
 void sort_node()
 {
@@ -1947,9 +1953,9 @@
 	if (vtysh)
 		return saved_ret;
 
-	/* This assumes all nodes above CONFIG_NODE are childs of CONFIG_NODE */
+	/* Go to parent for config nodes to attempt to find the right command */
 	while (ret != CMD_SUCCESS && ret != CMD_WARNING
-	       && vty->node > CONFIG_NODE) {
+	       && is_config(vty)) {
 		vty_go_parent(vty);
 		ret = cmd_execute_command_real(vline, vty, cmd);
 		tried = 1;
@@ -2097,7 +2103,7 @@
 		/* Try again with setting node to CONFIG_NODE */
 		while (ret != CMD_SUCCESS && ret != CMD_WARNING
 		       && ret != CMD_ERR_NOTHING_TODO
-		       && vty->node != CONFIG_NODE) {
+		       && vty->node != CONFIG_NODE && is_config(vty)) {
 			vty_go_parent(vty);
 			ret = cmd_execute_command_strict(vline, vty, NULL);
 		}