wifi: iwlwifi: move amsdu_size parsing to iwlwifi

The code that is parsing the amsdu_size module parameter and mapping it
to the corresponding Rx buffer size is common to all opmodes.
Move it into a function in iwlwifi, as preparation to a new op mode we
are working on.

Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Link: https://msgid.link/20240527190228.a3430d32923d.Iab3c22ef0df685f72f22dafc47021f0dc7bd6fa5@changeid


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