Update neutron-helm-overrides.yaml

Enable FDB learning for OVN as part of https://review.opendev.org/c/openstack/neutron/+/877675 which is observed once port security is disabled

Author: bjoernt

base-helm-configs/neutron/neutron-helm-overrides.yaml

@@ -246,6 +246,7 @@ conf:
       ovn_l3_scheduler: leastloaded
       ovn_nb_connection: "tcp:127.0.0.1:6641"
       ovn_sb_connection: "tcp:127.0.0.1:6642"
+      localnet_learn_fdb: true
     metadata_rate_limiting:
       rate_limit_enabled: true
       ip_versions: 4