Test neutron-dynamic-routing on OVN

With [0] and [1] merged, we no longer need to enforce using OVS for
testing neutron-dynamic-routing, but can use the default OVN setup
instead.

[0] https://review.opendev.org/c/openstack/neutron/+/864051
[1] https://review.opendev.org/c/openstack/neutron/+/738641

Change-Id: I6f6b3d020aebd7ac72b1b731dd3b4d369fc58d07
4 files changed