wifi: mac80211: ensure beacon is non-S1G prior to extracting the beacon timestamp field

Logic inside ieee80211_rx_mgmt_beacon accesses the
mgmt->u.beacon.timestamp field without first checking whether the beacon
received is non-S1G format.

Fix the problem by checking the beacon is non-S1G format to avoid access
of the mgmt->u.beacon.timestamp field.

Signed-off-by: Richard Kinder <richard.kinder@gmail.com>
Link: https://msgid.link/20240328005725.85355-1-richard.kinder@gmail.com


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