netlink: specs: fix indent in fou

Fix up the indentation. This has no functional effect, AFAICT.

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20230824003056.1436637-6-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>