wifi: mac80211: avoid non-S1G AID fallback for S1G assoc

wifi: mac80211: avoid non-S1G AID fallback for S1G assoc

When assoc_data->s1g is set and no AID Response element is present,
falling back to mgmt->u.assoc_resp.aid reads the non-S1G
association-response layout.

Keep the fallback for non-S1G only. If a successful S1G association
response omits the AID Response element, abandon the association
instead of proceeding with AID 0. Initialize aid to 0 for other S1G
responses so the later mask and logging flow keeps a defined value
without reading the non-S1G layout.

Fixes: 2a8a6b7c4cb0 ("wifi: mac80211: handle station association response with S1G")
Assisted-by: Codex:gpt-5.5
Assisted-by: Claude:claude-opus-4.8
Signed-off-by: Zhao Li <enderaoelyther@gmail.com>
Link: https://patch.msgid.link/20260612152440.25955-2-enderaoelyther@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>