core: include str.h in parse_param.h to avoid compile errors

- it happened when parse_param.h is used first, alone or without any
  predecessors including str.h

parser/parse_param.h

@@ -43,6 +43,7 @@
 
 #include <stdio.h>
 
+#include "../str.h"
 
 /*! \brief
  * Supported types of parameters