usbnet: Detect short packets as sent by the xHCI controller

The xHCI controller will ignore the endpoint MTU and so may deliver
packets of any length.  Detect short packets as being any packet that
has a length of zero or a length that is not a multiple of the MTU.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
Message-Id: <20220906183053.3625472-4-mcb30@ipxe.org>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/usb/dev-network.c

@@ -1211,7 +1211,7 @@ static void usb_net_handle_dataout(USBNetState *s, USBPacket *p)
     s->out_ptr += sz;
 
     if (!is_rndis(s)) {
-        if (p->iov.size < 64) {
+        if (p->iov.size % 64 || p->iov.size == 0) {
             qemu_send_packet(qemu_get_queue(s->nic), s->out_buf, s->out_ptr);
             s->out_ptr = 0;
         }