wifi-scripts: ucode: advertise SAE-EXT-KEY AKM alongside SAE

wifi-scripts: ucode: advertise SAE-EXT-KEY AKM alongside SAE

WPA3 Specification v3.5 §2.5.4 mandates that an AP's BSS Configuration
enables AKM suite selector 00-0F-AC:24 (SAE-EXT-KEY, SAE with a
group-dependent hash) whenever EHT or MLO is enabled. The WPA3 and
Wi-Fi Enhanced Open Deployment Guide v1.1 also recommends it on
non-EHT APs (Tables 3, 5, 6, 8).

Add a new sae_ext_key UCI option (enabled by default) that advertises
SAE-EXT-KEY, and FT-SAE-EXT-KEY when 802.11r is enabled, alongside
plain SAE/FT-SAE for the sae and psk-sae encryption modes.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Link: https://github.com/openwrt/openwrt/pull/23009
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>