mac80211: ignore country element TX power on 6 GHz

Updates to the 802.11ax draft are coming that deprecate the
country element in favour of the transmit power envelope
element, and make the maximum transmit power level field in
the triplets reserved, so if we parse them we'd use 0 dBm
transmit power.

Follow suit and completely ignore the element on 6 GHz for
purposes of determining TX power.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20201206145305.9abf9f6b4f88.Icb6e52af586edcc74f1f0360e8f6fc9ef2bfe8f5@changeid


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