make webusb tud_vendor_control_xfer_cb() weak by default to be overwritable for user sketch

Author: hathach

src/arduino/webusb/Adafruit_USBD_WebUSB.cpp

@@ -251,8 +251,9 @@ uint8_t const *tud_descriptor_bos_cb(void) { return desc_bos; }
 // Driver response accordingly to the request and the transfer stage
 // (setup/data/ack) return false to stall control endpoint (e.g unsupported
 // request)
-bool tud_vendor_control_xfer_cb(uint8_t rhport, uint8_t stage,
-                                tusb_control_request_t const *request) {
+TU_ATTR_WEAK bool
+tud_vendor_control_xfer_cb(uint8_t rhport, uint8_t stage,
+                           tusb_control_request_t const *request) {
   if (!_webusb_dev) {
     return false;
   }