netlink: specs: add ethnl PHY_GET command set

The PHY_GET command, supporting both DUMP and GET operations, is used to
retrieve the list of PHYs connected to a netdevice, and get topology
information to know where exactly it sits on the physical link.

Add the netlink specs corresponding to that command.

Signed-off-by: Maxime Chevallier <[e-mail]>
Reviewed-by: Christophe Leroy <[e-mail]>
Tested-by: Christophe Leroy <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/netlink/specs/ethtool.yaml

···
         - ovld-detected
         - power-not-available
         - short-detected
+  -
+    name: phy-upstream-type
+    enum-name:
+    type: enum
+    entries: [ mac, phy ]
 
 attribute-sets:
   -
···
       -
         name: total
         type: uint
+  -
+    name: phy
+    attributes:
+      -
+        name: header
+        type: nest
+        nested-attributes: header
+      -
+        name: index
+        type: u32
+      -
+        name: drvname
+        type: string
+      -
+        name: name
+        type: string
+      -
+        name: upstream-type
+        type: u32
+        enum: phy-upstream-type
+      -
+        name: upstream-index
+        type: u32
+      -
+        name: upstream-sfp-name
+        type: string
+      -
+        name: downstream-sfp-name
+        type: string
 
 operations:
   enum-model: directional
···
           - status-msg
           - done
           - total
+    -
+      name: phy-get
+      doc: Get PHY devices attached to an interface
+
+      attribute-set: phy
+
+      do: &phy-get-op
+        request:
+          attributes:
+            - header
+        reply:
+          attributes:
+            - header
+            - index
+            - drvname
+            - name
+            - upstream-type
+            - upstream-index
+            - upstream-sfp-name
+            - downstream-sfp-name
+      dump: *phy-get-op