Comment 4 for bug 1760584

The bug that was causing the OVN failure was fixed in https://review.openstack.org/#/c/559771/ - it changed the subnet cidr to a /29 so it should always succeed.

In reality it seems anything of /30 and smaller with DHCP enabled and a gateway attached is unusable, not sure if we need to validate that and return an error, the next IP allocation should fail with a reasonable error.