[neutron-tempest-plugin] Tag xena-last

Xena branch is in Extended Maintenance now[1]. Tempest and
tempest plugins are branchless which means master version of
Tempest and its plugins is used to test the supported stable
branches.

Once any stable branch is moved to EM state then, Tempest and
its plugins compatible tag[2] needs to be released so that we can
keep testing the EM stable branches with that tag once master
Tempest and its plugins are not compatible[3].

Tagging 'xena-last' as well as a new version also with same hash.

[1] https://releases.openstack.org/wallaby/index.html
[2] https://docs.openstack.org/tempest/latest/stable_branch_support_policy.html
[3] https://docs.openstack.org/tempest/latest/tempest_and_plugins_compatible_version_policy.html

Change-Id: I685e177dbc840d13ac1495b373e05c4e9575800b

deliverables/bobcat/neutron-tempest-plugin.yaml

@@ -14,3 +14,7 @@ releases:
     projects:
       - repo: openstack/neutron-tempest-plugin
         hash: 4330ca08687772aaa50867cc48668e2a17098aaf
+  - version: 2.4.0
+    projects:
+      - repo: openstack/neutron-tempest-plugin
+        hash: 604e5778935f928f32a142dc4875881c3605f011

deliverables/xena/neutron-tempest-plugin.yaml

@@ -22,3 +22,7 @@ releases:
     projects:
       - repo: openstack/neutron-tempest-plugin
         hash: da0daf3fc1113e55f22b20cf083d4f68218e4137
+  - version: xena-last
+    projects:
+      - repo: openstack/neutron-tempest-plugin
+        hash: 604e5778935f928f32a142dc4875881c3605f011