hostapd: add hostapd.conf param to force AP channel sync

When ap_channel_sync=1 the 40Mhz operating channel of an AP will be
set to the channel of an existing AP operating on the same PHY (NIC).

Signed-off-by: Arik Nemtsov <arik@wizery.com>
hostapd: use new op to sync AP channels

A new op will be used to get the operational frequency and secondary
channel of any existing APs, even if operating in different processes.

Use this op to select the channel for the current AP, if dictated by
the ap_channel_sync config parameter.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
driver_nl80211: implement shared AP channel op

Dump all AP interfaces using NL80211_CMD_GET_INTERFACE and make sure
the wiphy matches ours.

Signed-off-by: Arik Nemtsov <arik@wizery.com>