libnl-tiny: Generic Netlink multicast groups support

libnl-tiny: Generic Netlink multicast groups support

This adds this commit from normal libnl to libnl-tiny:
https://github.com/tgraf/libnl/commit/2dbc1ca76c5b82c40749e609eb83877418abb006

commit 2dbc1ca76c5b82c40749e609eb83877418abb006
Author: dima <dima.ky@gmail.com>
Date:   Wed Oct 13 17:53:34 2010 +0300

    Generic Netlink multicast groups support

    I have a patch against commit d378220c96c3c8b6f27dca33e7d8ba03318f9c2d
    extending libnl with a facility to receive generic netlink messages sent
    to multicast groups.

    Essentially it add one new function genl_ctrl_resolve_grp which
    prototype looks like this
    int genl_ctrl_resolve_grp(struct nl_sock *sk, const char *family_name,
            const char *grp_name)
    It resolves  the family name and the group name to group id. Then
    the returned id can be used in nl_socket_add_membership to subscribe
    to multicast messages.

    Besides that it adds two more functions

    uint32_t nl_socket_get_peer_groups(struct nl_sock *sk)
    void nl_socket_set_peer_groups(struct nl_sock *sk, uint32_t groups)

    allowing to modify the socket peer groups field. So it's possible to
    multicast messages from the user space using the legacy interface.
    Looks like there is no way (or I was not able to find one?) to modify
    the netlink socket destination group from the user space, when the
    group id is greater then 32.

Signed-off-by: Hauke Mehrtens <hauke.mehrtens@intel.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name> [cosmetic style fix]