Bluetooth: Add BT_DBG to mgmt_discovering()

This is helpful for device discovery implementation & debuging.
Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>

net/bluetooth/mgmt.c

@@ -3002,6 +3002,8 @@ int mgmt_discovering(struct hci_dev *hdev, u8 discovering)
 {
 	struct pending_cmd *cmd;
 
+	BT_DBG("%s discovering %u", hdev->name, discovering);
+
 	if (discovering)
 		cmd = mgmt_pending_find(MGMT_OP_START_DISCOVERY, hdev);
 	else