Comment 3 for bug 1629053

Ok, after discussing on IRC a bit more info.

my "normal bridge" backed device is tx-checksumming: on by default and work
my "ovs-dpdk" backed devices are tx-checksumming: off by default and work
my "normal ovs" backed devices are tx-checksumming: on by default and work as well

In E/N/I my interfaces only have (ens3 is the bridge backed one, and ens4 the one with an OVS of some kind):
auto ens3
iface ens3 inet dhcp
auto ens4
iface ens4 inet dhcp
So all defaults.

Versions for me:
libvirt-bin 2.1.0-1ubuntu6
qemu-kvm 1:2.6.1+dfsg-0ubuntu4

Sharing my network definitions for those:

Normal one:
    <interface type='network'>
      <mac address='52:54:00:3e:4b:48'/>
      <source network='default' bridge='virbr0'/>
      <target dev='vnet1'/>
      <model type='virtio'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>

OVS-DPDK one
    <interface type='vhostuser'>
      <mac address='52:54:00:99:f7:a4'/>
      <source type='unix' path='/var/run/openvswitch/vhost-user-2' mode='client'/>
      <model type='virtio'/>
      <alias name='net1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </interface>

With OVS-DPDK-multiqueue
    <interface type='vhostuser'>
      <mac address='52:54:00:d1:7e:cc'/>
      <source type='unix' path='/var/run/openvswitch/vhost-user-2' mode='client'/>
      <model type='virtio'/>
      <driver queues='4'/>
      <alias name='net1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </interface

With "pure" OVS checksumming:
    <interface type='bridge'>
      <mac address='52:54:00:b4:b4:1c'/>
      <source network='ovsbr0' bridge='ovsbr0'/>
      <virtualport type='openvswitch'>
        <parameters interfaceid='1c486148-a9ea-4000-8cfa-5fc9ce591f52'/>
      </virtualport>
      <target dev='vnet3'/>
      <model type='virtio'/>
      <driver name='vhost' queues='4'/>
      <alias name='net1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </interface>

The last should be your case, but with tx-checksumming: on it is working just nice.
I've run iperf, netperf and uperf over that connection all good.