[TF] Fix issue with missing NetworkIpAvailability extension.

In environment with TungstenFabric and enabled amphora provider.

Related-PROD: PRODX-30528
Change-Id: I63c36c3c23d920f12f4823062990227844f2bf49
(cherry picked from commit 2f7eee6f505c2ec5d067f2c5ae040e41033e6401)
(cherry picked from commit cea9b6babcb43d98ca58f2b73689df7a8a028864)
diff --git a/octavia_tempest_plugin/config.py b/octavia_tempest_plugin/config.py
index 0eb773a..44f864c 100644
--- a/octavia_tempest_plugin/config.py
+++ b/octavia_tempest_plugin/config.py
@@ -15,6 +15,7 @@
 
 from oslo_config import cfg
 from oslo_log import log as logging
+from tempest import config
 
 from octavia_tempest_plugin.common import constants as const
 
@@ -310,3 +311,12 @@
                      'scope? This configuration value should be same as '
                      'octavia.conf: [oslo_policy].enforce_scope option.'),
 ]
+
+
+def is_tungstenfabric_backend_enabled():
+    """Return True if TungstenFabric is used as a backend."""
+    try:
+        sdn = getattr(config.CONF, 'sdn')
+        return getattr(sdn, 'service_name', None) == 'tungstenfabric'
+    except cfg.NoSuchOptError:
+        return False