cfg80211: reject HT/VHT capabilities on 6 GHz band

On the 6 GHz band, HE should be used, but without any direct HT/VHT
capabilities, instead the HE 6 GHz band capabilities will capture
the relevant information. Reject HT/VHT capabilities here.

Link: https://lore.kernel.org/r/20200528213443.bfe89c35459a.Ibba5e066fa0087fd49d13cfee89d196ea0c68ae2@changeid


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