release note update

Author: g0rgamesh

releasenotes/notes/enable_ovn-b84974f398242dcb.yaml

@@ -2,4 +2,7 @@
 upgrade:
   - |
     Enabled ML2/OVN by default as checks preventing accidental migration
-    from ML2/OVS were added in kolla-ansible.
+    from ML2/OVS were added in kolla-ansible. If you are using a Neutron
+    plugin other than ML2/OVN, set `kolla_enable_ovn` to `false`.
+    OVN distributed FIP is also enabled, to disable it set
+    `neutron_ovn_distributed_fip` to `false`.