* RESTCONF strict namespace validation of data in POST and PUT.

* Accepted:
  ```
    curl -X PUT http://localhost/restconf/data/mod:a -d {"mod:a":"x"}
  ```
  * Not accepted (must prefix "a" with module):
  ```
    curl -X PUT http://localhost/restconf/data/mod:a -d {"a":"x"}
  ```
  * Undefine `RESTCONF_NS_DATA_CHECK` in include/clixon_custom.h to disable strict check.

include/clixon_custom.h

@@ -44,3 +44,7 @@
 /* Use new xml_insert code on sorted xml lists
  */
 #define USE_XML_INSERT
+
+/* Make namespace check on RESTCONF PUT and POST -d data
+ */
+#define RESTCONF_NS_DATA_CHECK