docs: def generate_local_port():
      """https://github.com/thom311/libnl/blob/libnl3_2_25/lib/socket.c#L63."""
      global _PREVIOUS_LOCAL_PORT
      if _PREVIOUS_LOCAL_PORT is None:
          try:
              with contextlib.closing(socket.socket(getattr(socket, 'AF_NETLINK', -1), socket.SOCK_RAW)) as s:
                  s.bind((0, 0))
                  _PREVIOUS_LOCAL_PORT = int(s.getsockname()[0])
          except OSError:
              _PREVIOUS_LOCAL_PORT = 4294967295  # UINT32_MAX
      return int(_PREVIOUS_LOCAL_PORT)