It looks like your cake is new enough to support set associative hashing,
but not the new overhead handling. The ATM flag was put in a long time ago.

Looking at the code which grabs those options (cake_change), there doesn't
seem to be a way to detect whether an unsupported option was provided by
userspace, unless nla_parse_nested returns an error if the provided option
struct would be overflowed. Clearly it doesn't, but just truncates it to
fit.

- Jonathan Morton