The function hostapd_event_ch_switch() derived the seg0_idx and seg1_idx
values only for the 5 GHz and 2.4 GHz bands and the 6 GHz case ended up
using incorrect calculation based on the 5 GHz channel definitions.
Fix this by adding support for 6 GHz frequencies.
Signed-off-by: Rohan <drohan@codeaurora.org>