geneve, specs: Add port range to rt_link specification

Add the port range to rt_link, example:

# tools/net/ynl/pyynl/cli.py --spec Documentation/netlink/specs/rt_link.yaml \
--do getlink --json '{"ifname": "geneve1"}' --output-json | jq
{
"ifname": "geneve1",
[...]
"linkinfo": {
"kind": "geneve",
"data": {
"id": 1000,
"remote": "147.28.227.100",
"udp-csum": 0,
"ttl": 0,
"tos": 0,
"label": 0,
"df": 0,
"port": 49431,
"udp-zero-csum6-rx": 1,
"ttl-inherit": 0,
"port-range": {
"low": 4000,
"high": 5000
}
}
},
[...]
}

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://patch.msgid.link/20250226182030.89440-2-daniel@iogearbox.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>