iwlwifi: api: annotate compressed BA notif array sizes

Annotate the compressed BA notification array sizes and
make both of them 0-length since the length of 1 is just
confusing - it may be different than that and the offset
to the second one needs to be calculated in the C code
anyhow.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>