Comment 22 for bug 1533876

Reviewed: https://review.openstack.org/289370
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=98464d54d0fcdba452191bc0291d59957c9cdae6
Submitter: Jenkins
Branch: stable/liberty

commit 98464d54d0fcdba452191bc0291d59957c9cdae6
Author: Sean Mooney <email address hidden>
Date: Fri Jan 22 17:00:36 2016 +0000

    stop setting mtu when plugging vhost-user ports

    vhost-user is a userspace protocol to establish connectivity
    between a virto-net frontend typically qemu and a
    userspace virtio backend such as ovs with dpdk.

    vhost-user interfaces exist only in userspace from the host perspective
    and are not represented in the linux networking stack as kernel netdevs.
    As a result attempting to set the mtu on a vhost-user interface
    using ifconfig or ip link will fail with a device not found error.

    - this change removes a call to _set_device_mtu when plugging
      vhost-user interfaces.
    - this change prevents the device not found error from occurring
      which stopped vms booting with vhost-user interfaces
      due to an uncaught exception resulting in a failure to set the
      interface type in ovs.
    - this change make creating vhost-user interface
      an atomic action.

    This latent bug is only triggered when the mtu value is set to a
    value other than 0 which was the default proir to mitaka.

    Conflicts:
     nova/network/model.py
     nova/tests/unit/virt/libvirt/test_vif.py
     nova/virt/libvirt/vif.py

    Change-Id: I2e17723d5052d57cd1557bd8a173c06ea0dcb2d4
    Closes-Bug: #1533876
    (cherry picked from commit adf7ba61dd73fe4bfffa20295be9a4b1006a1fe6)