code: def _function_add_node(self, cfg_node, function_addr):
          
          snippet = self._to_snippet(cfg_node=cfg_node)
          self.kb.functions._add_node(function_addr, snippet)
docs: Adds node to function manager, converting address to CodeNode if
          possible
  
          :param CFGNode cfg_node:    A CFGNode instance.
          :param int function_addr:   Address of the current function.
          :return: None