Implement nested snat validation test scenario

It's disabled for ovn because it's not, yet, implemented for the driver.

See: https://review.opendev.org/c/openstack/neutron/+/926495

(The feature also requires special configuration for the driver that we
probably won't enable in the gate. This can be discussed though.)

Related-Bug: #2051935
Change-Id: Ie2e49a53857009446e22300e2fff292355cef058
diff --git a/neutron_tempest_plugin/config.py b/neutron_tempest_plugin/config.py
index a6d5c09..d259201 100644
--- a/neutron_tempest_plugin/config.py
+++ b/neutron_tempest_plugin/config.py
@@ -77,6 +77,11 @@
                default='openstackgate.local',
                help='dns_domain value configured at neutron.conf, which will '
                     'be used for the DNS configuration of the instances'),
+    cfg.BoolOpt('snat_rules_apply_to_nested_networks',
+                default=False,
+                help='Whether SNAT rules apply recursively to all connected '
+                'networks. This is the default behavior for ovs and '
+                'linuxbridge drivers.'),
 
     # Multicast tests settings
     cfg.StrOpt('multicast_group_range',