wifi: iwlwifi: mvm: use min_t() for agg_size

We can use min_t() for the agg_size and avoid
spelling out the (firmware) limit twice.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230620125813.211768036c1f.I78b7eea32eaae20cc9f32869aa3f42814634ce9a@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>