nl80211: support setting S1G channels

nl80211: support setting S1G channels

S1G channels have a single width defined per frequency, so
derive it from the channel flags with
ieee80211_s1g_channel_width().

Also support setting an S1G channel where control frequency may
differ from operating, and add some basic validation to
ensure the control channel is with the operating.

Signed-off-by: Thomas Pedersen <thomas@adapt-ip.com>
Link: https://lore.kernel.org/r/20200908190323.15814-6-thomas@adapt-ip.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>