cfg80211: treat 6 GHz channels as valid regardless of capability

If a 6 GHz channel exists, then we can probably safely assume that
the device actually supports it, and then it should support most
bandwidths.

This will probably need to be extended to check the interface type
and then dig into the HE capabilities for that though, to have the
correct bandwidth check.

Link: https://lore.kernel.org/r/20200528213443.d4864ef52e92.I82f09b2b14a56413ce20376d09967fe954a033eb@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>