iwlwifi: mvm: add missing min_size to kernel-doc

On struct iwl_rx_handlers we should document the min_size
member, do that.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/iwlwifi.20211219110000.0c42c428bc6b.I8bfa49d534acc5f513f2fb3dff2d6f22f6c45071@changeid