Mark multicast scenario test as unstable for now

Change-Id: I034ad37d9fb0a92c31a3403e1ecaf48ca93b33ab
Related-Bug: #1850288
diff --git a/neutron_tempest_plugin/scenario/test_multicast.py b/neutron_tempest_plugin/scenario/test_multicast.py
index 9b79582..d511b3b 100644
--- a/neutron_tempest_plugin/scenario/test_multicast.py
+++ b/neutron_tempest_plugin/scenario/test_multicast.py
@@ -229,6 +229,7 @@
         server['ssh_client'].execute_script(
             'echo "%s" > ~/multicast_traffic_receiver.py' % check_script)
 
+    @utils.unstable_test("bug 1850288")
     @decorators.idempotent_id('113486fc-24c9-4be4-8361-03b1c9892867')
     def test_multicast_between_vms_on_same_network(self):
         """Test multicast messaging between two servers on the same network