Set RF path direction to "off" when transceiver_mode is OFF.

firmware/hackrf_usb/hackrf_usb.c

@@ -223,6 +223,7 @@ void set_transceiver_mode(const transceiver_mode_t new_transceiver_mode) {
 	} else {
 		gpio_clear(PORT_LED1_3, PIN_LED2);
 		gpio_clear(PORT_LED1_3, PIN_LED3);
+		rf_path_set_direction(RF_PATH_DIRECTION_OFF);
 		max2837_stop();
 		return;
 	}