fel: Fix USB timeout on large transfers

Trying to use oversized initrd files (20 MB or more) can fail
with the "libusb usb_bulk_send error -1" error message.

To address this problem, we can split the transfer into smaller
chunks and the problem disappears. Effectively, this is a revert
of the older "fel: Increase timeout to 60 seconds instead of
splitting bulk transfers" commmit.
Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>

fel.c

@@ -73,11 +73,14 @@ static void pr_info(const char *fmt, ...)
 	}
 }
 
+static const int AW_USB_MAX_BULK_SEND = 4 * 1024 * 1024; // 4 MiB per bulk request
+
 void usb_bulk_send(libusb_device_handle *usb, int ep, const void *data, int length)
 {
 	int rc, sent;
 	while (length > 0) {
-		rc = libusb_bulk_transfer(usb, ep, (void *)data, length, &sent, timeout);
+		int len = length < AW_USB_MAX_BULK_SEND ? length : AW_USB_MAX_BULK_SEND;
+		rc = libusb_bulk_transfer(usb, ep, (void *)data, len, &sent, timeout);
 		if (rc != 0) {
 			fprintf(stderr, "libusb usb_bulk_send error %d\n", rc);
 			exit(2);