netkit: Add add netkit scrub support to rt_link.yaml

Add netkit scrub attribute support to the rt_link.yaml spec file.

Example:

  # ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/rt_link.yaml \
   --do getlink --json '{"ifname": "nk0"}' --output-json | jq
  [...]
  "linkinfo": {
    "kind": "netkit",
    "data": {
      "primary": 0,
      "policy": "forward",
      "mode": "l3",
      "scrub": "default",
      "peer-policy": "forward",
      "peer-scrub": "default"
    }
  },
  [...]

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Nikolay Aleksandrov <razor@blackwall.org>

Documentation/netlink/specs/rt_link.yaml

@@ -920,6 +920,13 @@ definitions:
       - name: l2
       - name: l3
 
+  -
+    name: netkit-scrub
+    type: enum
+    entries:
+      - name: none
+      - name: default
+
 attribute-sets:
   -
     name: link-attrs
@@ -2147,6 +2154,14 @@ attribute-sets:
         name: mode
         type: u32
         enum: netkit-mode
+      -
+        name: scrub
+        type: u32
+        enum: netkit-scrub
+      -
+        name: peer-scrub
+        type: u32
+        enum: netkit-scrub
 
 sub-messages:
   -