mac80211: build HE operation with 6 GHz oper information

Add 6 GHz operation information (IEEE 802.11ax/D6.0, Figure 9-787k)
while building HE operation element for non-HE AP. This field is used to
determine channel information in the absence of HT/VHT IEs.

Signed-off-by: Rajkumar Manoharan <rmanohar@codeaurora.org>
Link: https://lore.kernel.org/r/1589399105-25472-8-git-send-email-rmanohar@codeaurora.org
[fix skb allocation size]
Link: https://lore.kernel.org/r/20200528193455.76796-1-johannes@sipsolutions.net


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