nl80211: Explicitly differentiate between 5 GHz and 6 GHz modes

nl80211: Explicitly differentiate between 5 GHz and 6 GHz modes

When a device supports both the 5 GHz band and the 6 GHz band,
these are reported as two separate modes, both with mode set to
HOSTAPD_MODE_IEEE80211A. However, as these are different modes,
each with its own characteristics, e.g., rates, capabilities etc.,
specifically differentiate between them by adding a flag to indicate
whether the mode describes a 6 GHz band capabilities or not.

Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>