usb: usbtest: support bos descriptor test for usb 3.0

In Test 9 of usbtest module, it is used for performing chapter 9 tests N
times. This patch adds to support getting bos descriptor test scenario for
USB 3.0.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>