Rectify test_ipv6_subnet_override option

Related-Bug: PRODX-17659
Change-Id: Icc377c43e19d2b3e31c05213962b76235fae8b46
diff --git a/octavia_tempest_plugin/tests/test_base.py b/octavia_tempest_plugin/tests/test_base.py
index d071393..ea8ad54 100644
--- a/octavia_tempest_plugin/tests/test_base.py
+++ b/octavia_tempest_plugin/tests/test_base.py
@@ -263,9 +263,9 @@
             cls.lb_member_2_subnet = override_subnet
 
             if (CONF.load_balancer.test_with_ipv6 and
-                    conf_lb.test_IPv6_subnet_override):
+                    conf_lb.test_ipv6_subnet_override):
                 override_ipv6_subnet = show_subnet(
-                    conf_lb.test_IPv6_subnet_override)
+                    conf_lb.test_ipv6_subnet_override)
                 cls.lb_member_vip_ipv6_subnet = override_ipv6_subnet
                 cls.lb_member_1_ipv6_subnet = override_ipv6_subnet
                 cls.lb_member_2_ipv6_subnet = override_ipv6_subnet