def genlmsg_attrdata(gnlh, hdrlen):
return nlattr(genlmsg_user_data(gnlh, hdrlen))<EOL>
Return nlattr at the start of message attributes.

    https://github.com/thom311/libnl/blob/libnl3_2_25/lib/genl/genl.c#L287

    Positional arguments:
    gnlh -- Generic Netlink message header (genlmsghdr class instance).
    hdrlen -- length of user header (integer).

    Returns:
    nlattr class instance with others in its payload.