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: ddd1ad68 ("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.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>