netlink: specs: rtnetlink: attribute naming corrections

Some attribute names diverge in very minor ways from the C names.
These are most likely typos, and they prevent the C codegen from
working.

Fixes: bc515ed0 ("netlink: specs: Add a spec for neighbor tables in rtnetlink")
Fixes: b2f63d90 ("doc/netlink: Add spec for rt link messages")
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20250414211851.602096-7-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>