Unify checks for TF backend

Method of checking already presented in the tempest.
We can only reuse it.

Related-Prod: PRODX-37464
Change-Id: I5e75582081843a0530094c4f2ee0ce32360b31c0
diff --git a/octavia_tempest_plugin/tests/test_base.py b/octavia_tempest_plugin/tests/test_base.py
index 79c8bf0..19b827c 100644
--- a/octavia_tempest_plugin/tests/test_base.py
+++ b/octavia_tempest_plugin/tests/test_base.py
@@ -34,7 +34,6 @@
 
 from octavia_tempest_plugin.common import cert_utils
 from octavia_tempest_plugin.common import constants as const
-from octavia_tempest_plugin import config as config_octavia
 from octavia_tempest_plugin.tests import RBAC_tests
 from octavia_tempest_plugin.tests import validators
 from octavia_tempest_plugin.tests import waiters
@@ -863,7 +862,7 @@
             cls.webserver2_public_ip))
 
         if (CONF.load_balancer.test_with_ipv6 and not
-                config_octavia.is_tungstenfabric_backend_enabled()):
+                config.is_tungstenfabric_backend_enabled()):
             # Enable the IPv6 nic in webserver 1
             cls._enable_ipv6_nic_webserver(
                 cls.webserver1_public_ip, cls.lb_member_keypair['private_key'],
@@ -1043,7 +1042,7 @@
                 network_id=network['id'],
                 mac_address=instance_network[0]['OS-EXT-IPS-MAC:mac_addr'])
             port_id = result['ports'][0]['id']
-            if config_octavia.is_tungstenfabric_backend_enabled():
+            if config.is_tungstenfabric_backend_enabled():
                 port = result['ports'][0]
                 fixed_ip = None
                 for ip in port["fixed_ips"]: