docs: def nlmsg_attrdata(nlh, hdrlen):
      """Head of attributes data.
  
      https://github.com/thom311/libnl/blob/libnl3_2_25/lib/msg.c#L143
  
      Positional arguments:
      nlh -- Netlink message header (nlmsghdr class instance).
      hdrlen -- length of family specific header (integer).
  
      Returns:
      First attribute (nlattr class instance with others in its payload).
      """
      data = nlmsg_data(nlh)
      return libnl.linux_private.netlink.nlattr(bytearray_ptr(data, libnl.linux_private.netlink.NLMSG_ALIGN(hdrlen)))