code: def nlmsg_append(n, data, len_, pad):
      
      tmp = nlmsg_reserve(n, len_, pad)
      if tmp is None:
          return -NLE_NOMEM
      tmp[:len_] = data.bytearray[:len_]
      _LOGGER.debug('msg 0x%x: Appended %d bytes with padding %d', id(n), len_, pad)
      return 0
docs: Append data to tail of a Netlink message.
  
      https://github.com/thom311/libnl/blob/libnl3_2_25/lib/msg.c#L442
  
      Extends the Netlink message as needed and appends the data of given length to the message.
  
      Positional arguments:
      n -- Netlink message (nl_msg class instance).
      data -- data to add.
      len_ -- length of data (integer).
      pad -- number of bytes to align data to (integer).
  
      Returns:
      0 on success or a negative error code.