nixos/hostapd: set default channel to auto

The current default, 7, is, to put it nicely, absolutely ridiculous.

On 2.4 GHz, the only channels you should use are 1, 6 and 11, because
every other channel overlaps one of those and causes interference.

On 5/6 GHz, channel 7 does not exist at all.

Also, it's 2024, most things will support automatic channel selection,
and those that don't will likely need extra care to support prehistoric
hardware anyway.

Author: K900

nixos/modules/services/networking/hostapd.nix

@@ -235,7 +235,7 @@ in {
             };
 
             channel = mkOption {
-              default = 7;
+              default = 0;
               example = 11;
               type = types.int;
               description = ''