Feature Request: 5GHz DFS Channel Support

DFS is more important in US than pretty much anywhere in the world due to strict FCC ruling around U-NII-2A band. Take a look at a great table of channels summary on wiki: https://en.wikipedia.org/wiki/List_of_WLAN_channels#5_GHz_(802.11a/h/j/n/ac/ax) it shows three big things:

• The majority of the spectrum requires DFS (channels 50-144)
• In order to run 160Mhz you must use DFS channels (or use 80+80 mode which is actually a unicorn)
• To use pretty standard 80Mhz you have very small amount of non-DFS which will be congested horribly in any condominium

DFS isn't exactly a new shiny thing which was just introduced and people need to adapt. It has been with us for over a decade:

In 2007, the FCC (United States) began requiring that devices operating in the bands of 5.250–5.350 GHz and 5.470–5.725 GHz must employ dynamic frequency selection (DFS) and transmit power control (TPC) capabilities.

It has been years since I used any ISP-provided hardware and I personally opt for solutions from Ruckus, MikroTik, or Cisco. However, as this isn't representative I simply did a spectral scan in my house. There are 67 networks on the 5Ghz band. Around half of them operate within the DFS range. We don't have Verizon FIOS here but looking at SSIDs XFinity/Comcast devices indeed avoid DFS channels while AT&T devices prefer them. 

Pretty much every manufacturer supports DFS in their AP gear, especially in higher models. Listing companies doesn't make sense here really as I can reply "any besides those who cheaped-out on FCC certification" as any 5Ghz 802.11ac-supporting chip on the market supports DFS (and there pretty much four player here: Broadcom, Atheros, Intel, and Realtek). One of the OEMs making consumer and prosumer devices will be Netgear which even have a convenient table, listing pretty much every device they make in the last decade: https://kb.netgear.com/000060372/Which-NETGEAR-devices-support-Dynamic-Frequency-Selection

Samsung S21 does support DFS as a client and I see them connect to our corporate network on the daily basis, as some of the APs must run on DFS channels due to congestion. Every single Apple device I've seen since the draft-ac days also works with DFS channels. I have two ATVs (4K models) in my own house and I can assure you they do support connecting to a network running DFS channels, as this is the only 5Ghz network I run. To my knowledge there's no extra certification needed to support DFS & TPC channels from the client perspective, you just need to be certified to operate in that frequency range. There are only extra steps to support DFS as an AP, and here's where Roku cheaped-out.