usbnet: add new flag FLAG_NOARP for usb net devices

We do have some USB net devices, which cannot do ARP.
so we can introduce a new flag FLAG_NOARP, then client drivers
can easily handle this kind of devices

Signed-off-by: Wei Shuai <cpuwolf@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/usb/usbnet.h b/include/linux/usb/usbnet.h
index bd45eb7..5de7a22 100644
--- a/include/linux/usb/usbnet.h
+++ b/include/linux/usb/usbnet.h
@@ -100,6 +100,7 @@
 #define FLAG_LINK_INTR	0x0800		/* updates link (carrier) status */
 
 #define FLAG_POINTTOPOINT 0x1000	/* possibly use "usb%d" names */
+#define FLAG_NOARP	0x2000		/* device can't do ARP */
 
 /*
  * Indicates to usbnet, that USB driver accumulates multiple IP packets.