mac80211: add HE 6 GHz Band Capabilities into parse extension

Handle 6 GHz band capability element parsing for association.

Signed-off-by: Rajkumar Manoharan <rmanohar@codeaurora.org>
Link: https://lore.kernel.org/r/1589399105-25472-4-git-send-email-rmanohar@codeaurora.org
[some renaming to be in line with previous patches]
Link: https://lore.kernel.org/r/20200528213443.a13d7a0b85b0.Ia07584da4fc77aa77c4cc563248d2ce4234ffe5d@changeid


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