wifi: mac80211: set ieee80211_prep_tx_info::link_id upon Auth Rx

wifi: mac80211: set ieee80211_prep_tx_info::link_id upon Auth Rx

This will be used by the low level driver.
Note that link_id  will be 0 in case of a non-MLO authentication.
Also fix a call-site of mgd_prepare_tx() where the link_id was not
populated.

Update the documentation to reflect the current state
ieee80211_prep_tx_info::link_id is also available in mgd_complete_tx().

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250205110958.6a590f189ce5.I1fc5c0da26b143f5b07191eb592f01f7083d55ae@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>