Bluetooth: use hdev lock in activate_scan for hci_is_adv_monitoring

hci_is_adv_monitoring's function documentation states that it must be
called under the hdev lock. Paths that leads to an unlocked call are:
discov_update => start_discovery => interleaved_discov => active_scan
and: discov_update => start_discovery => active_scan

The solution is to take the lock in active_scan during the duration of
the call to hci_is_adv_monitoring.

Fixes: c32d6246 ("Bluetooth: disable filter dup when scan for adv monitor")
Signed-off-by: Niels Dossche <dossche.niels@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/hci_request.c

@@ -2260,6 +2260,7 @@ static int active_scan(struct hci_request *req, unsigned long opt)
 	if (err < 0)
 		own_addr_type = ADDR_LE_DEV_PUBLIC;
 
+	hci_dev_lock(hdev);
 	if (hci_is_adv_monitoring(hdev)) {
 		/* Duplicate filter should be disabled when some advertisement
 		 * monitor is activated, otherwise AdvMon can only receive one
@@ -2276,6 +2277,7 @@ static int active_scan(struct hci_request *req, unsigned long opt)
 		 */
 		filter_dup = LE_SCAN_FILTER_DUP_DISABLE;
 	}
+	hci_dev_unlock(hdev);
 
 	hci_req_start_scan(req, LE_SCAN_ACTIVE, interval,
 			   hdev->le_scan_window_discovery, own_addr_type,