tools: ynl: remove the libmnl dependency

We don't use libmnl any more.

Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Link: https://lore.kernel.org/r/20240227223032.1835527-15-kuba@kernel.org


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