nixos/network-interfaces: Add support for multiple ipv4 / ipv6 addresses
nixos/network-interfaces: Add flush upon interface going down
Refactor nixos files relying on the old ipAddress / prefixLength / subnetMask attributes
nixos/network-interfaces: Support the old ip configuration convention
Merge pull request #3182 from wkennington/master.ipv6

nixos/network-interfaces: Add support for multiple ipv4 / ipv6 addresses