Backport of commit 7a560a1a5769 ("iwinfo: add 802.11ax HE support").
enables 802.11ax capability detection through ubus in OpenWrt 21.02
(e.g. with MT7915E 802.11ax PCI Express Wireless Network Adapter)
Signed-off-by: Šimon Bořek <simon.borek@nic.cz>
[commit message facelift, use openwrt-21.02 branch]
Signed-off-by: Petr Štetiar <ynezz@true.cz>