Use unified function to check for TF backend

Related-Prod: PRODX-37464
Change-Id: Icad71d674f1c3460729a6945393858986d5799da
(cherry picked from commit c79954b8255ef40322c16c4bb6fad2ff4d31905d)
diff --git a/tempest/api/network/admin/test_routers.py b/tempest/api/network/admin/test_routers.py
index 60e6218..d8ef4a3 100644
--- a/tempest/api/network/admin/test_routers.py
+++ b/tempest/api/network/admin/test_routers.py
@@ -141,7 +141,7 @@
 
     def _verify_gateway_port(self, router_id):
         # Workaround for PRODX-8489
-        if CONF.get('sdn').get('service_name') == "tungstenfabric":
+        if config.is_tungstenfabric_backend_enabled():
             self._wait_for_ports(router_id)
         list_body = self.admin_ports_client.list_ports(
             network_id=CONF.network.public_network_id,
diff --git a/tempest/api/network/test_security_groups.py b/tempest/api/network/test_security_groups.py
index 41a0ecb..e6d0f7e 100644
--- a/tempest/api/network/test_security_groups.py
+++ b/tempest/api/network/test_security_groups.py
@@ -192,7 +192,7 @@
         port_range_min = 77
         port_range_max = 77
 
-        if CONF.get('sdn').get('service_name') == "tungstenfabric":
+        if config.is_tungstenfabric_backend_enabled():
             if self.ethertype == 'IPv6':
                 remote_ip_prefix = '::/0'
             else:
@@ -229,7 +229,7 @@
         protocol = 'ipv6-icmp' if self._ip_version == 6 else 'icmp'
         icmp_type_codes = [(3, 2), (3, 0), (8, 0), (0, 0), (11, None)]
         for icmp_type, icmp_code in icmp_type_codes:
-            if CONF.get('sdn').get('service_name') == "tungstenfabric":
+            if config.is_tungstenfabric_backend_enabled():
                 if self.ethertype == 'IPv6':
                     remote_ip_prefix = '::/0'
                 else: