Import dhcpcd-6.4.3 with the following changes:

  *  Correct DHCPv6 Prefix Delegation option decoding
  *  Poll interfaces on BSD for IFF_RUNNING if link state cannot be obtained
  *  Check for an IA to use in DHCPv6 lease validation
  *  Warn about exceeding IDGEN_RETRIES when a stable private address cannot
     be obtained
  *  Fix DHCP option overload handling, thanks to Tobias Stoeckmann