We use the lifetime of 0 to indicate permanent addresses while
DHCP uses that lifetime to indicate the addresses should be removed.
Use the presence of a timestamp to differentiate the two.

  dhclient[10867]: XMT: Rebind on wls1, interval 1030ms.
  dhclient[10867]: RCV: Reply message on wls1 from fe80::21e:8cff:feec:3ca2.
  NetworkManager[10481]: <info>  [1478020967.7634] dhcp6 (wls1):   valid_lft 0
  NetworkManager[10481]: <info>  [1478020967.7634] dhcp6 (wls1):   preferred_lft 0
  NetworkManager[10481]: <info>  [1478020967.7636] dhcp6 (wls1):   address fd25:d463:2f14::927
  NetworkManager[10481]: <info>  [1478020967.7636] dhcp6 (wls1):   nameserver 'fe80::21e:8cff:feec:3ca2'
  NetworkManager[10481]: <info>  [1478020967.7637] dhcp (wls1):   domain search 'venom.'
  NetworkManager[10481]: <info>  [1478020967.7637] dhcp6 (wls1): state changed unknown -> bound, event ID="fa:cd:2c:86|1478020967"
  NetworkManager[10481]: ((src/nm-core-utils.c:3521)): assertion '<dropped>' failed