netlink: specs: Add missing bridge linkinfo attrs

Attributes for FDB learned entries were added to the if_link netlink api
for bridge linkinfo but are missing from the rt_link.yaml spec. Add the
missing attributes to the spec.

Fixes: ddd1ad6882 ("net: bridge: Add netlink knobs for number / max learned FDB entries")
Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20240503164304.87427-1-donald.hunter@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/netlink/specs/rt_link.yaml

@@ -1144,6 +1144,12 @@ attribute-sets:
       -
         name: mcast-querier-state
         type: binary
+      -
+        name: fdb-n-learned
+        type: u32
+      -
+        name: fdb-max-learned
+        type: u32
   -
     name: linkinfo-brport-attrs
     name-prefix: ifla-brport-