mac80211: Fix radiotap header channel flag for 6GHz band

Radiotap header field 'Channel flags' has '2 GHz spectrum' set to
'true' for 6GHz packet.
Change it to 5GHz as there isn't a separate option available for 6GHz.

Signed-off-by: Aloka Dixit <alokad@codeaurora.org>
Link: https://lore.kernel.org/r/010101747ab7b703-1d7c9851-1594-43bf-81f7-f79ce7a67cc6-000000@us-west-2.amazonses.com


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