pvusb: add missing definition to usbif.h

The pvusb request structure contains the transfer_flags member which
is missing definitions of it's semantics.

Add the definition of the USBIF_SHORT_NOT_OK flag.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>

xen/include/public/io/usbif.h

@@ -187,6 +187,7 @@ struct usbif_urb_request {
 	/* basic urb parameter */
 	uint32_t pipe;
 	uint16_t transfer_flags;
+#define USBIF_SHORT_NOT_OK	0x0001
 	uint16_t buffer_length;
 	union {
 		uint8_t ctrl[8]; /* setup_packet (Ctrl) */