Add {head,tail}room attributes to rt-link.yaml spec file.

Example:

$ tools/net/ynl/pyynl/cli.py \
  --spec Documentation/netlink/specs/rt-link.yaml \
  --do getlink --json '{"ifname":"enp0s1"}' --output-json \
  | jq -r '{ifname,mtu,headroom,tailroom}'
{
  "ifname": "enp0s1",
  "mtu": 1500,
  "headroom": 12,
  "tailroom": 0
}

Signed-off-by: Alasdair McWilliam <alasdair@mcwilliam.dev>
Reviewed-by: Daniel Borkmann <daniel@iogearbox.net>
---
 Documentation/netlink/specs/rt-link.yaml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/netlink/specs/rt-link.yaml b/Documentation/netlink/specs/rt-link.yaml
index 6ab31f86854d..2a23e9699c0b 100644
--- a/Documentation/netlink/specs/rt-link.yaml
+++ b/Documentation/netlink/specs/rt-link.yaml
@@ -1057,6 +1057,12 @@ attribute-sets:
       -
         name: netns-immutable
         type: u8
+      -
+        name: headroom
+        type: u16
+      -
+        name: tailroom
+        type: u16
   -
     name: prop-list-link-attrs
     subset-of: link-attrs
-- 
2.47.3