Comment 1 for bug 1720175

this is currently not used by anyting in os-vif so we should remove it before anything uses it incorrectly.
as pointed out this is legacy code form when the subnet object was imported for nova networks originally and it is only used for firwalling when not using neutron.

in the legacy nova-networks code path currently nova does not use the os-vif object when creating the firewall rules, only when pluging the interface so there is no use of these field in nova either so its safe to remove them from the subnet object in os-vif.