[RFC AP: ACS: select primary channel for 5G-band based on interference factor

[Марков Михаил Александрович]

>Can you please share hostapd debug logs for a case with and without this
>patch highlighting why this is needed?
With https://pastebin.com/WVeeBiDD
Without https://pastebin.com/VLZhJf3S
Both times VHT80 requested.

>And it would be called unconditionally for VHT and HE.. Is that really
>correct? What if the configuration is requesting 20 MHz channel
>bandwidth to be used?
I can not say for sure how would it work for HE, but if i use HT20 it
works correctly. Here is `iw dev' output:
phy#3
	Interface wlan1
		ifindex 12
		wdev 0x300000002
		addr 7a:f0:82:62:19:11
		ssid xxx
		type AP
		channel 40 (5200 MHz), width: 20 MHz, center1: 5200 MHz
		txpower 20.00 dBm
		multicast TXQ:
			qsz-byt	qsz-pkt	flows	drops	marks	...
			0	0	0	0	0

I do realize that setting "conf->secondary_channel to be != 0" could be
not the best decision, but `allowed_ht40_channel_pair' check messes
everything. That's why i tried to RFC.