hostapd: expose beacon reports through ubus

hostapd: expose beacon reports through ubus

Subscribe to beacon reports through ubus.
Can be used for hearing map and client steering purposes.

First enable rrm:
    ubus call hostapd.wlan0 bss_mgmt_enable '{"beacon_report":True}'

Subscribe to the hostapd notifications via ubus.

Request beacon report:
    ubus call hostapd.wlan0 rrm_beacon_req
	'{"addr":"00:xx:xx:xx:xx:xx", "op_class":0, "channel":1,
	"duration":1,"mode":2,"bssid":"ff:ff:ff:ff:ff:ff", "ssid":""}'

Signed-off-by: Nick Hainke <vincent@systemli.org>
[rework identation]
Signed-off-by: David Bauer <mail@david-bauer.net>