Enable execution of experimental linuxbridge job

During the Zed PTG it was decided to handle unsupported features in
Neutron as experimental. See section titled "When we say something is
not supported?", day 2 in [1].

The first feature to be handled this way is the linuxbridge ML2 driver,
see [2]. In this patch, the execution of linuxbridge jobs is enabled
under the experimental framework

[1] https://lists.openstack.org/pipermail/openstack-discuss/2022-April/028164.html
[2] https://review.opendev.org/c/openstack/neutron/+/845181

Change-Id: Id4bf385acaacbaeb308f5e9b1e0f1e22a9b1bbef
1 file changed