Fix HT40 co-ex scan for some pri/sec channel switches

Fix HT40 co-ex scan for some pri/sec channel switches

Secondary channel was compared incorrectly (-4/4 vs. actual channel
number) which broke matching neighboring 40 MHz BSSes and only the
no-beacons-on-secondary-channel rule was applied in practice. Once
sec_chan was fixed, this triggered another issue in this function where
both rules to switch pri/sec channels could end up getting applied in a
way that effectively canceled the switch.

Signed-off-by: Jouni Malinen <j@w1.fi>