I was able to add vhostuserclientport directly to a VM.

1. There was a problem with apparmor, I had to give it rw access to the place I wanted to create the vhost socket.
   For example, this is how I did it. I'm sure there's a better way:
   Add these two lines to /etc/apparmor.d/libvirt/libvirt-f80091e1-f0d1-412b-a58a-e1c25be3d4f8.files
   "/run/" rwk,
   "/var/run/" rwk,
   Then,
   apparmor_parser -r /etc/apparmor.d/libvirt/libvirt-f80091e1-f0d1-412b-a58a-e1c25be3d4f8

2. Create the xml

       <interface type='vhostuser'>
         <mac address='00:00:00:00:00:01'/>
         <source type='unix' path='/var/run/dpdkvhostuserclient0' mode='server'/>
         <model type='virtio'/>
         <driver queues='2'/>
       </interface>
   

3. Attach it to the vm

   virsh attach-device --domain instance-00000084 --live --config --file vhostuserclient0.xml

BTW. /var/run/dpdkvhostuserclient0 is from creating the port (and first the bridge)

ovs-vsctl add-br br0_dpdk -- set bridge br0_dpdk datapath_type=netdev
ovs-vsctl add-port br0_dpdk vhostuserclient0 -- set Interface vhostuserclient0 type=dpdkvhostuserclient options:vhost-server-path=/var/run/dpdkvhostuserclient0 ofport_request=1

BUT STILL!
1. I don't understand how I get ovs-dpdk implementation for "free". Normal traffic between the vms stay low
2. This is using ovs-vsctl - how do I do that in the formal openstack way?