usbnet: allow "minidriver" to prevent urb unlinking on usbnet_stop

rndis_wlan devices freeze after running usbnet_stop several times. It appears
that firmware freezes in state where it does not respond to any RNDIS commands
and device have to be physically unplugged/replugged. This patch lets
minidrivers to disable unlink_urbs on usbnet_stop through new info flag.

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/include/linux/usb/usbnet.h b/include/linux/usb/usbnet.h
index 7c17b2e..c642f78 100644
--- a/include/linux/usb/usbnet.h
+++ b/include/linux/usb/usbnet.h
@@ -86,6 +86,7 @@
 
 #define FLAG_FRAMING_AX 0x0040		/* AX88772/178 packets */
 #define FLAG_WLAN	0x0080		/* use "wlan%d" names */
+#define FLAG_AVOID_UNLINK_URBS 0x0100	/* don't unlink urbs at usbnet_stop() */
 
 
 	/* init device ... can sleep, or cause probe() failure */