Cover both enabled and disabled cases in nested snat validation test

Check connectivity when nested SNAT is enabled; expect no connectivity otherwise.

Change-Id: I50cbdc50a6689a7dada10c5a00233afd4ee6c93a
diff --git a/zuul.d/master_jobs.yaml b/zuul.d/master_jobs.yaml
index 8a45e3a..b8d2103 100644
--- a/zuul.d/master_jobs.yaml
+++ b/zuul.d/master_jobs.yaml
@@ -683,6 +683,10 @@
               type_drivers: local,flat,vlan,geneve
             ml2_type_vlan:
               network_vlan_ranges: foo:1:10,public
+            ovn:
+              # This feature is available in OVN v24.03.4
+              # Latest Ubuntu 24.04 provides OVN v24.03.2
+              ovn_router_indirect_snat: false
         test-config:
           $TEMPEST_CONFIG:
             network-feature-enabled: