usb: allow max 8192 bytes for desc

A device of USB video class usually uses larger desc structure, so
use larger buffer to avoid failure. (dev-video.c is ready)

This is an unlikely code path:
1, during guest startup, guest tries to probe device.
2, run 'lsusb' command in guest(or other similar commands).

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
Message-Id: <20220112015835.900619-1-pizhenwei@bytedance.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>