tree schema UPDATE schema mount support for lys_getnext

... which also adds the support for lys_find_xpath_atoms().
diff --git a/src/xpath.h b/src/xpath.h
index 3e61bb0..c34a0f3 100644
--- a/src/xpath.h
+++ b/src/xpath.h
@@ -381,6 +381,7 @@
                                                              warning is printed. */
 #define LYXP_ACCESS_TREE_ALL 0x80   /**< Explicit accessible tree of all the nodes. */
 #define LYXP_ACCESS_TREE_CONFIG 0x0100  /**< Explicit accessible tree of only configuration data. */
+#define LYXP_SCNODE_SCHEMAMOUNT LYS_FIND_SCHEMAMOUNT    /**< Nodes from mounted modules are also accessible. */
 
 /**
  * @brief Cast XPath set to another type.