Comment 6 for bug 1543094

I don't see good way to fix compare-and-swap in ipam driver to be at least as good as locking approach, so I propose to revert commit d755f7248d324bb4c44b3efc9d200f8eb075066d.

And fix original issue with missed lock by:
https://review.openstack.org/#/c/223123/1/neutron/ipam/drivers/neutrondb_ipam/db_api.py