wifi: mac80211: do not permit 40 MHz EHT operation on 5/6 GHz

wifi: mac80211: do not permit 40 MHz EHT operation on 5/6 GHz

The EHT PHY requirements state that 80 MHz must be supported on the 5
and 6 GHz bands unless the STA is 20 MHz only. So if the channel width
is limited to 40 MHz on a band other than 2.4 GHz, then disable EHT and
downgrade to HE.

The primary case where this can happen is if the hardware disables
puncturing using IEEE80211_HW_DISALLOW_PUNCTURING.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Cc: stable@vger.kernel.org
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250826202553.a6582f3abf57.Ic670429dc7127f68c818b4290d950ebfb5a0b9e1@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>