netlink: specs: rt-link: Add attributes for hsr

netlink: specs: rt-link: Add attributes for hsr

YNL wasn't able to decode the linkinfo from hsr interfaces. Add the
linkinfo attribute definitions for hsr interfaces. Example output now
looks like this:

$ ynl --spec Documentation/netlink/specs/rt-link.yaml --do getlink \
    --json '{"ifname": "hsr0"}' --output-json | jq .linkinfo
{
  "kind": "hsr",
  "data": {
    "slave1": 15,
    "slave2": 13,
    "supervision-addr": "01:15:4e:00:01:00",
    "seq-nr": 64511,
    "version": 1,
    "protocol": 0
  }
}

Signed-off-by: Felix Maurer <fmaurer@redhat.com>
Link: https://patch.msgid.link/926077a70de614f1539c905d06515e258905255e.1762968225.git.fmaurer@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>