staging: wfx: implement start_ap/stop_ap

staging: wfx: implement start_ap/stop_ap

Currently, wfx_bss_info_changed() check interface status changes and
guess when the pattern match with an AP start and AP stop (through
wfx_update_beaconing()). It is far easier to rely on start_ap and
stop_ap callbacks provided by mac80211.

wfx_bss_info_changed() keeps only the responsibility of updating the
frame templates.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200410133239.438347-5-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>