The hwsim SendFrame method requires the radio frequency which
is obtained from the hostapd config file. This adds a generic
API to get any config value from the hostapd config, as well
as a get_freq API that converts the channel number to a
frequency.
For testing SA Query, the autotest needs the ablility to force
kill (and restart) hostapd without giving it time to deauth its
stations gracefully. A method was added to the HostapdCLI class
which does a killall -9 hostapd, resets the wlnX interface,
and restarts hostapd with the same arguments as it had before.
Make the HostapdCLI class non-static so that each objects corresponds
to a hostapd instance on one network interface (this is independent of
whether the AP instances use one or separate hostapd processes)
