Enhance get_mode() to return correct hw_mode with 6 GHz support

Enhance get_mode() to return correct hw_mode with 6 GHz support

The 5 GHz channels are stored in one hw_features set with mode
HOSTAPD_MODE_IEEE80211A while the 6 GHz channels will need to be stored
in a separate hw_features set (but with same mode
HOSTAPD_MODE_IEEE80211A) due to possibility of different HT/VHT/HE
capabilities being available between the 5 GHz and 6 GHz bands.

Iterate through all hw_features sets and check and match the band of
channel supported by the hw_features set while getting the hw_features
set in get_mode(). This allows both the 5 GHz and 6 GHz channels to be
found and correct capabilities to be used in cases where the driver
reports different capability values between 5 and 6 GHz channels.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>