plugins ext FEATURE initial schema-mount support

Only for XML data for now. Includes lots of other
changes needed to support this extension.
diff --git a/src/plugins_exts/yangdata.c b/src/plugins_exts/yangdata.c
index 0c96a14..55a03e3 100644
--- a/src/plugins_exts/yangdata.c
+++ b/src/plugins_exts/yangdata.c
@@ -172,10 +172,10 @@
 
         .plugin.id = "libyang 2 - yang-data, version 1",
         .plugin.compile = &yangdata_compile,
-        .plugin.parse = NULL,
-        .plugin.validate = NULL,
         .plugin.sprinter = &yangdata_schema_printer,
-        .plugin.free = yangdata_free
+        .plugin.free = yangdata_free,
+        .plugin.parse = NULL,
+        .plugin.validate = NULL
     },
     {0}     /* terminating zeroed record */
 };