wifi: mac80211: mlme: unify CSA handling

Unify all the CSA handling, including handling of a beacon
after the CSA, into ieee80211_sta_process_chanswitch().

The CRC of the beacon will change due to changes in the
CSA/ECSA elements, so there's really no need to have the
'beacon after CSA' handling before the CRC processing or
to change the beacon_crc_valid value here.

Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240228095719.e269c0e02905.I9dc68ff1e84d51349822bc7d3b33b578fcf8e360@changeid


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