USB: gadget: fix rndis regression

Restore some code that was wrongly dropped from the RNDIS
driver, and caused interop problems observed with OpenMoko.

The issue is with hardware which needs help conforming to part
of the USB 2.0 spec (section 8.5.3.2); some can automagically
send a ZLP in response to an unexpected IN, but not all chips
will do that.  We don't need to check the packet length ourselves
the way earlier code did, since the UDC must already check it.
But we do need to tell the UDC when it must force a short packet
termination of the data stage.

(Based on a patch from Aric D. Blumer <aric at sdgsystems.com>)
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/f_rndis.c

@@ -437,7 +437,7 @@ invalid:
 		DBG(cdev, "rndis req%02x.%02x v%04x i%04x l%d\n",
 			ctrl->bRequestType, ctrl->bRequest,
 			w_value, w_index, w_length);
-		req->zero = 0;
+		req->zero = (value < w_length);
 		req->length = value;
 		value = usb_ep_queue(cdev->gadget->ep0, req, GFP_ATOMIC);
 		if (value < 0)