netlink: specs: Introduce new netlink command to list available time stamping layers

Add a new commands allowing to list available time stamping layers on a
netdevice's link.

Example usage :
./ynl/cli.py --spec netlink/specs/ethtool.yaml --no-schema \
	     --do ts-list-get \
	     --json '{"header":{"dev-name":"eth0"}}'
{'header': {'dev-index': 3, 'dev-name': 'eth0'},
 'ts-list-layer': b'\x01\x00\x00\x00\x05\x00\x00\x00'}
Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/netlink/specs/ethtool.yaml

@@ -949,6 +949,16 @@ attribute-sets:
       -
         name: ts-layer
         type: u32
+  -
+    name: ts-list
+    attributes:
+      -
+        name: header
+        type: nest
+        nested-attributes: header
+      -
+        name: ts-list-layer
+        type: binary
 
 operations:
   enum-model: directional
@@ -1713,3 +1723,17 @@ operations:
           attributes: &ts
             - header
             - ts-layer
+    -
+      name: ts-list-get
+      doc: Get list of timestamp devices available on an interface
+
+      attribute-set: ts-list
+
+      do:
+        request:
+          attributes:
+            - header
+        reply:
+          attributes:
+            - header
+            - ts-list-layer