Mark test_floatingip_port_details test as unstable

Change-Id: I52f5552807c889c63a8583b2bfc124e9c89fca6f
Related-Bug: #1815585
diff --git a/neutron_tempest_plugin/scenario/test_floatingip.py b/neutron_tempest_plugin/scenario/test_floatingip.py
index be57475..15a2837 100644
--- a/neutron_tempest_plugin/scenario/test_floatingip.py
+++ b/neutron_tempest_plugin/scenario/test_floatingip.py
@@ -212,6 +212,7 @@
     def resource_setup(cls):
         super(FloatingIPPortDetailsTest, cls).resource_setup()
 
+    @common_utils.unstable_test("bug 1815585")
     @decorators.idempotent_id('a663aeee-dd81-492b-a207-354fd6284dbe')
     def test_floatingip_port_details(self):
         """Tests the following: