Description of problem:
When USB mass storage device is connected to client, it's redirected into guest, even mass storage class is bocked by filter string. 
This happens only when spice-xpi page is used.

Guest recognize USB mass storage media with proper class: 
bInterfaceClass         8 Mass Storage
Qemu-kvm on host logs connected device:
attaching high speed device 0951:162d version 1.0 class 00
And device is redirected even filter log is used:
USB Filter String was set to: '"8,-1,-1,-1,0"'

If client is connected via command line:
remote-viewer spice://localhost?port=3334 --spice-usbredir-auto-redirect-filter="8,-1,-1,-1,0"
everything is fine and USB is not redirected.

Version-Release number of selected component (if applicable):
spice-server-0.12.4-3.el7.x86_64
spice-vdagent-0.14.0-5.el7.x86_64
spice-gtk3-0.20-6.el7.x86_64
spice-xpi-2.8-4.el7.x86_64
spice-glib-0.20-6.el7.x86_64
usbredir-0.6-5.el7.x86_64

How reproducible:
Always from spice xpi test page http://people.freedesktop.org/~teuf/test.html

Steps to Reproduce:
1.Go to spice xpi test page http://people.freedesktop.org/~teuf/test.html
2.Fill in host, port, usb listen port to 0, usb autoredirect, usb filter to "8,-1,-1,-1,0" (blocking USB class 8)
3.Connect to guest
4.Plug USB mass storage device into client

Actual results:
USB is redirected into guest

Expected results:
USB is not redirected into guest

Additional info:
Host: RHEL7 64
Client: RHEL7 64
Guest: Win7 64, RHEL7 64