libyang BUGFIX don't access LYS_EXT ->parent

In lys_is_disabled() we must stop iterating to ->parent when we are on a
LYS_EXT node because its parent pointer is not a lys_node.  This fixes
the Debian unit test failures on big-endian systems.

src/tree_schema.c

@@ -108,6 +108,8 @@ lys_is_disabled(const struct lys_node *node, int recursive)
             /* unresolved augment, let's say it's enabled */
             return NULL;
         }
+    } else if (node->nodetype == LYS_EXT) {
+        return NULL;
     } else if (node->parent) {
         node = node->parent;
     } else {