hostap: fix incorrect link mode selection for SAP

When SAP runs on hostapd, the HE (11ax) capability should be determined
based on hw_mode->he_capab, which reflects the Wi-Fi FW capability.
Using conf->ieee80211ax is incorrect because it only represents the
default value derived from build-time configuration macros, and does not
accurately represent real hardware capabilities.
Same change is also needed for VHT and HT check.

Signed-off-by: Maochen Wang <maochen.wang@nxp.com>