tools: ynl: give up on libmnl for auto-ints

The temporary auto-int helpers are not really correct.
We can't treat signed and unsigned ints the same when
determining whether we need full 8B. I realized this
before sending the patch to add support in libmnl.
Unfortunately, that patch has not been merged,
so time to fix our local helpers. Use the mnl* name
for now, subsequent patches will address that.

Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20240227223032.1835527-2-kuba@kernel.org


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