This patch adds the support of queues attribute of the driver element
for vhost-user interface type. Example:

<interface type='vhostuser'>
      <mac address='52:54:00:ee:96:6d'/>
      <source type='unix' path='/tmp/vhost2.sock' mode='client'/>
      <model type='virtio'/>
      <driver queues='4'/>
</interface>

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1207692Signed-off-by: NMaxime Leroy <maxime.leroy@6wind.com>
Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>