Cherry pick Neutron fix for enable_ipset breakage

This adds a cherry pick for a Neutron enable_ipset default
setting update that recently broke Overcloud deployments.

See the neutron patch here:

https://review.openstack.org/#/c/121434/

Change-Id: Ib88c7601378e83e0352271f7ff7180a75a3fe811
Related-bug: #1369381