wifi-scripts: ucode: default the SAE-EXT-KEY AKM per WPA3 mode

wifi-scripts: ucode: default the SAE-EXT-KEY AKM per WPA3 mode

Commit a12cec9ea3c8 ("wifi-scripts: ucode: advertise SAE-EXT-KEY AKM
alongside SAE") advertised the SAE-EXT-KEY AKM (00-0F-AC:24, SAE using a
group-dependent hash, aka SAE-GDH) by default on every sae, sae-mixed and
sae-compat BSS.

WPA3 Specification v3.5 only makes this AKM mandatory when the BSS enables
EHT or MLO (section 2.5, item 4); for HE and below it is merely
recommended (sections 2.2 and 2.3). In practice the FT-SAE-EXT-KEY AKM
(SAE-EXT-KEY combined with 802.11r), which gets added automatically once
Fast Transition is enabled, keeps some clients from associating (a Samsung
Galaxy Tab S10 FE) or makes them reboot shortly after connecting (a Poco
X6). Plain SAE-EXT-KEY without FT was seen to work on the same tablet, but
its interoperability is not well tested.

Drop the fixed schema default and pick the default from the auth type in
parse_encryption instead. Only default it on where it is both mandatory
and safe to offer: on Compatibility mode (sae-compat) BSSes running an EHT
htmode, which carry it in a separate RSN Override element that legacy
clients ignore. Keep it off for WPA3-Personal (sae) and Transition
(sae-mixed) mode, where it would sit in the main RSNE that a choking
client cannot ignore, and off on non-EHT BSSes. An explicit
'option sae_ext_key 0/1' still overrides this per BSS.

The SAE-EXT-KEY AKM in the sae-compat RSN Override 2 element now keys off
config.sae_ext_key alone; the extra config.rsn_override_pairwise_2 guard
is dropped, decoupling the AKM from the GCMP-256 pairwise cipher so each
follows its own option.

Fixes: a12cec9ea3c8 ("wifi-scripts: ucode: advertise SAE-EXT-KEY AKM alongside SAE")
Assisted-by: Claude:claude-opus-4-8
Link: https://github.com/openwrt/openwrt/pull/24041
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>