mac80211: add radar detection command/event

Add command to trigger radar detection in the driver/FW.
Once radar detection is started it should continuously
monitor for radars as long as the channel active.
If radar is detected usermode notified with 'radar
detected' event.

Scanning and remain on channel functionality must be disabled
while doing radar detection/scanning, and vice versa.

Based on original patch by Victor Goldenshtein <victorg@ti.com>

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
index 6d0b89e..43a45cf 100644
--- a/net/mac80211/scan.c
+++ b/net/mac80211/scan.c
@@ -351,6 +351,9 @@
 static bool ieee80211_can_scan(struct ieee80211_local *local,
 			       struct ieee80211_sub_if_data *sdata)
 {
+	if (local->radar_detect_enabled)
+		return false;
+
 	if (!list_empty(&local->roc_list))
 		return false;