wifi: mac80211: update outdated comment

wifi: mac80211: update outdated comment

The function ieee80211_start_scan() was refactored and replaced by
__ieee80211_start_scan() in commit f3b85252f081 ("mac80211: fix scan
races and rework scanning"). Update the comment in
ieee80211_tx_h_check_assoc() accordingly.

Additionally, remove the broken gmane.org link in the comment.

Suggested-by: Lachlan Hodges <lachlan.hodges@morsemicro.com>
Suggested-by: Johannes Berg <johannes@sipsolutions.net>
Assisted-by: unnamed:deepseek-v3.2 coccinelle
Signed-off-by: Kexin Sun <kexinsun@smail.nju.edu.cn>
Link: https://patch.msgid.link/20260228061944.887-1-kexinsun@smail.nju.edu.cn
Signed-off-by: Johannes Berg <johannes.berg@intel.com>