yanglint FEATURE extdata cmd for interactive mode

Implementation of --ext-data parameter for interactive yanglint mode.
diff --git a/tools/lint/common.c b/tools/lint/common.c
index 1ba4a1d..f2ff464 100644
--- a/tools/lint/common.c
+++ b/tools/lint/common.c
@@ -27,6 +27,7 @@
 
 #include "compat.h"
 #include "libyang.h"
+#include "plugins_exts.h"
 
 int
 parse_schema_path(const char *path, char **dir, char **module)
@@ -937,3 +938,19 @@
     free(module_name);
     return parent_node;
 }
+
+LY_ERR
+ext_data_clb(const struct lysc_ext_instance *ext, void *user_data, void **ext_data, ly_bool *ext_data_free)
+{
+    struct ly_ctx *ctx;
+    struct lyd_node *data = NULL;
+
+    ctx = ext->module->ctx;
+    if (user_data) {
+        lyd_parse_data_path(ctx, user_data, LYD_XML, LYD_PARSE_STRICT, LYD_VALIDATE_PRESENT, &data);
+    }
+
+    *ext_data = data;
+    *ext_data_free = 1;
+    return LY_SUCCESS;
+}