Import dhcpcd-6.4.1 with the following changes:

  *  If just given a domain and no search list, make the search list the domain
  *  Skip arpping directives if we have a profile but not parsing one
  *  Allow the request of a DHCPv6 address or prefix, a prefix length must be
     specified
  *  Add the ability to dump DHCPv6 leases
  *  Improve startup with regards to carrier checking and adding a link-local
     IPv6 address
  *  Start the correct interface reference for added devices
  *  Support
     http://datatracker.ietf.org/doc/draft-ietf-dhc-dhcpv6-stateful-issues-06
     via the ia_pd_mix option
  *  Fix link handling where kernel reported flags in LINK_UP may not be
     valid when we actually process them
  *  Fix defining new options in dhcpcd.conf and requesting them
  *  Fix a potential segfault when reloading configurations
  *  Print user defined options via -V
  *  Add support for RFC6603, Prefix Exclude option
  *  When requesting a IA_PD and another IA type, create a psuedo interface
     to handle the IA_PD
  *  Handle truncated DHCPv6 saved leases