Import dhcpcd-6.6.6 with the following changes:
  *  Clarify timeout and reboot timeout, make it more sane
  *  A server should not NAK an INFORM
  *  The noalias directive will now remove any IPv4 addresses existing on
     the interface when we want to add our own
  *  Stop polling for IPv6 router reachability
     Instead, expect for cached neighour route additions/changes/removals
     to be announced by the kernel
  *  Store acquired time for each IPv6 address so we can correctly offset
     pltime and vltime if we need to re-add them