docs: def print_genl_hdr(ofd, start):
      """https://github.com/thom311/libnl/blob/libnl3_2_25/lib/msg.c#L821.
  
      Positional arguments:
      ofd -- function to call with arguments similar to `logging.debug`.
      start -- bytearray() or bytearray_ptr() instance.
      """
      ghdr = genlmsghdr(start)
      ofd('  [GENERIC NETLINK HEADER] %d octets', GENL_HDRLEN)
      ofd('    .cmd = %d', ghdr.cmd)
      ofd('    .version = %d', ghdr.version)
      ofd('    .unused = %#d', ghdr.reserved)