usbmon vs. tcpdump: fix dropped packet count

Report the number of dropped packets instead of zero
when using the binary usbmon interface with tcpdump.

# tcpdump -i usbmon1 -w dump
tcpdump: listening on usbmon1, link-type USB_LINUX_MMAPPED (USB with padded Linux header), capture size 65535 bytes
^C2155 packets captured
2155 packets received by filter
1019 packets dropped by kernel

Signed-off-by: Johannes Stezenbach <js@sig21.net>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/mon/mon_bin.c

@@ -1101,7 +1101,7 @@ static long mon_bin_ioctl(struct file *file, unsigned int cmd, unsigned long arg
 		nevents = mon_bin_queued(rp);
 
 		sp = (struct mon_bin_stats __user *)arg;
-		if (put_user(rp->cnt_lost, &sp->dropped))
+		if (put_user(ndropped, &sp->dropped))
 			return -EFAULT;
 		if (put_user(nevents, &sp->queued))
 			return -EFAULT;