Skip iptables act/stby test based on topology set

Task: 35877
Story: 2006260

Change-Id: I53671c7e93737b0d7bc038b4dd136a179facd34a
diff --git a/octavia_tempest_plugin/common/constants.py b/octavia_tempest_plugin/common/constants.py
index 7ddcb7a..e767298 100644
--- a/octavia_tempest_plugin/common/constants.py
+++ b/octavia_tempest_plugin/common/constants.py
@@ -97,6 +97,7 @@
 SORT = 'sort'
 SINGLE = 'SINGLE'
 ACTIVE_STANDBY = 'ACTIVE_STANDBY'
+SUPPORTED_LB_TOPOLOGIES = (SINGLE, ACTIVE_STANDBY)
 
 # Protocols
 HTTP = 'HTTP'