ynl: skip rendering attributes with header property in uapi mode

To allow omitting some of the attributes in the final generated file.

Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20241204155549.641348-3-sdf@fomichev.me


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