tools: ynl: fix header guards

tools: ynl: fix header guards

devlink and ethtool have a trailing _ in the header guard. I must have
copy/pasted it into new guards, assuming it's a headers_install artifact.

This fixes build if system headers are old.

Fixes: 8f109e91b852 ("tools: ynl: include dpll and mptcp_pm in C codegen")
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20240222234831.179181-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>