Comment 1 for bug 1961173

The fact that it only fails for conntrack scenario and even before Local IP creation makes me think it might be related to iptables_hybrid firewall driver used for this scenario.
Looking at comments [1] and [2] I remembered that iptables_hybrid lacks isolation between hosts in fullstack tests. Since local_ip test uses 2 hosts we better use noop firewall for conntrack scenario.

[1] https://github.com/openstack/neutron/blob/3dfe6072421e3d5dc708a3bf065fb1a64ea3129a/neutron/tests/fullstack/test_securitygroup.py#L96

[2] https://github.com/openstack/neutron/blob/3dfe6072421e3d5dc708a3bf065fb1a64ea3129a/neutron/tests/fullstack/test_securitygroup.py#L536