extensions CHANGE optimise use of padding bytes in complex extension instance

copy pointer to some of the plugin's commonly used data into the extension
instance structure to simplify accessing it while using padding space which
must be present but tha wouldn't be used otherway.
diff --git a/src/tree_schema.c b/src/tree_schema.c
index 8a40588..d5839bc 100644
--- a/src/tree_schema.c
+++ b/src/tree_schema.c
@@ -1084,7 +1084,7 @@
     unsigned int u;
 
     for (u = start; u < ext_size; u++) {
-        if (ext[u]->substmt == substmt) {
+        if (ext[u]->insubstmt == substmt) {
             return u;
         }
     }
@@ -1128,6 +1128,7 @@
             case LYEXT_COMPLEX:
                 result[u] = calloc(1, ((struct lyext_plugin_complex*)orig[u]->def->plugin)->instance_size);
                 ((struct lys_ext_instance_complex*)result[u])->module = mod;
+                ((struct lys_ext_instance_complex*)result[u])->substmt = ((struct lyext_plugin_complex*)orig[u]->def->plugin)->substmt;
                 /* TODO duplicate data in extension instance content */
                 break;
             case LYEXT_ERR:
@@ -1140,8 +1141,8 @@
             result[u]->arg_value = lydict_insert(mod->ctx, orig[u]->arg_value, 0);
             result[u]->parent = parent;
             result[u]->parent_type = parent_type;
-            result[u]->substmt = orig[u]->substmt;
-            result[u]->substmt_index = orig[u]->substmt_index;
+            result[u]->insubstmt = orig[u]->insubstmt;
+            result[u]->insubstmt_index = orig[u]->insubstmt_index;
 
             /* extensions */
             orig[u]->ext = NULL;
@@ -1428,7 +1429,7 @@
         return NULL;
     }
 
-    switch (ext->substmt) {
+    switch (ext->insubstmt) {
     case LYEXT_SUBSTMT_SELF:
     case LYEXT_SUBSTMT_MODIFIER:
     case LYEXT_SUBSTMT_VERSION:
@@ -1440,9 +1441,9 @@
         break;
     case LYEXT_SUBSTMT_BASE:
         if (ext->parent_type == LYEXT_PAR_TYPE) {
-            return ((struct lys_type*)ext->parent)->info.ident.ref[ext->substmt_index];
+            return ((struct lys_type*)ext->parent)->info.ident.ref[ext->insubstmt_index];
         } else if (ext->parent_type == LYEXT_PAR_IDENT) {
-            return ((struct lys_ident*)ext->parent)->base[ext->substmt_index];
+            return ((struct lys_ident*)ext->parent)->base[ext->insubstmt_index];
         }
         break;
     case LYEXT_SUBSTMT_BELONGSTO:
@@ -1472,7 +1473,7 @@
             case LYS_LEAFLIST:
                 /* in case of leaf, the index is supposed to be 0, so it will return the
                  * correct pointer despite the leaf structure does not have dflt as array */
-                return ((struct lys_node_leaflist*)ext->parent)->dflt[ext->substmt_index];
+                return ((struct lys_node_leaflist*)ext->parent)->dflt[ext->insubstmt_index];
             case LYS_CHOICE:
                 return ((struct lys_node_choice*)ext->parent)->dflt;
             default:
@@ -1482,9 +1483,9 @@
         } else if (ext->parent_type == LYEXT_PAR_TPDF) {
             return ((struct lys_tpdf*)ext->parent)->dflt;
         } else if (ext->parent_type == LYEXT_PAR_DEVIATE) {
-            return ((struct lys_deviate*)ext->parent)->dflt[ext->substmt_index];
+            return ((struct lys_deviate*)ext->parent)->dflt[ext->insubstmt_index];
         } else if (ext->parent_type == LYEXT_PAR_REFINE) {
-            return &((struct lys_refine*)ext->parent)->dflt[ext->substmt_index];
+            return &((struct lys_refine*)ext->parent)->dflt[ext->insubstmt_index];
         }
         break;
     case LYEXT_SUBSTMT_DESCRIPTION:
@@ -1675,9 +1676,9 @@
         break;
     case LYEXT_SUBSTMT_UNIQUE:
         if (ext->parent_type == LYEXT_PAR_DEVIATE) {
-            return &((struct lys_deviate*)ext->parent)->unique[ext->substmt_index];
+            return &((struct lys_deviate*)ext->parent)->unique[ext->insubstmt_index];
         } else if (ext->parent_type == LYEXT_PAR_NODE && ((struct lys_node*)ext->parent)->nodetype == LYS_LIST) {
-            return &((struct lys_node_list*)ext->parent)->unique[ext->substmt_index];
+            return &((struct lys_node_list*)ext->parent)->unique[ext->insubstmt_index];
         }
         break;
     case LYEXT_SUBSTMT_UNITS:
@@ -4342,7 +4343,7 @@
         }
 
         if (e[i]->def && e[i]->def->plugin && e[i]->def->plugin->type == LYEXT_COMPLEX) {
-            substmt = ((struct lyext_plugin_complex *)e[i]->def->plugin)->substmt;
+            substmt = ((struct lys_ext_instance_complex *)e[i])->substmt;
             for (j = 0; substmt[j].stmt; j++) {
                 switch(substmt[j].stmt) {
                 case LY_STMT_DESCRIPTION: