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
diff --git a/zuul.d/master_jobs.yaml b/zuul.d/master_jobs.yaml
index 7bb7149..0ac6bbd 100644
--- a/zuul.d/master_jobs.yaml
+++ b/zuul.d/master_jobs.yaml
@@ -496,6 +496,8 @@
               l3_ha: true
             AGENT:
               debug_iptables_rules: true
+            EXPERIMENTAL:
+              linuxbridge: true
           # NOTE(slaweq): We can get rid of this hardcoded absolute path when
           # devstack-tempest job will be switched to use lib/neutron instead of
           # lib/neutron-legacy