parser json FEATURE support for nested ext instances with data

... such as schema-mount.
diff --git a/src/validation.c b/src/validation.c
index 5699c8d..8004b44 100644
--- a/src/validation.c
+++ b/src/validation.c
@@ -1330,6 +1330,11 @@
 
     /* validate all restrictions of nodes themselves */
     LY_LIST_FOR_SAFE(first, next, node) {
+        if (node->flags & LYD_EXT) {
+            /* ext instance data should have already been validated */
+            continue;
+        }
+
         if (!node->parent && mod && (lyd_owner_module(node) != mod)) {
             /* all top-level data from this module checked */
             break;