From: Eugene Syromiatnikov <redacted>
Date: Mon, 7 Jan 2019 16:22:29 +0100

Otherwise it is impossible to use it for something else, as it will break
userspace that puts garbage there.

The same check should be done in other structures, but the fact that
data in reserved fields is ignored is already part of the kernel ABI.

Signed-off-by: Eugene Syromiatnikov <redacted>

I think the opportunity to enforce this has passed and you will break
userspace by doing this.