ipsec: infra for selecting backends

Change-Id: Ifa6d8391b1b2413a88b7720fc434e0bc849a149a
Signed-off-by: Klement Sekera <ksekera@cisco.com>
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>

test/template_ipsec.py

@@ -95,6 +95,11 @@ class TemplateIpsec(VppTestCase):
     vpp_esp_protocol = 1
     vpp_ah_protocol = 0
 
+    @classmethod
+    def ipsec_select_backend(cls):
+        """ empty method to be overloaded when necessary """
+        pass
+
     @classmethod
     def setUpClass(cls):
         super(TemplateIpsec, cls).setUpClass()
@@ -106,6 +111,7 @@ class TemplateIpsec(VppTestCase):
             i.resolve_arp()
             i.config_ip6()
             i.resolve_ndp()
+        cls.ipsec_select_backend()
 
     def tearDown(self):
         super(TemplateIpsec, self).tearDown()