eldbus-cxx: Fixed infinite recursion with post-increment operator

The pre-increment operator was being defined twice and being
implemented as a post-increment. Modified declaration to be
post-increment as it was supposed to be.

src/bindings/eldbus_cxx/eldbus_message.hh

@@ -77,7 +77,7 @@ struct message_iterator
       }
     return *this;
   }
-  message_iterator operator++() const
+  message_iterator operator++(int)
   {
     message_iterator tmp(*this);
     ++*this;