Import dhcpcd-6.0.3 with the following changes:
* dhcpcd will now assign a short hostname by default
  To use a FQDN hostname, set this in dhcpcd.conf(5)
  env hostname_fqdn=YES
* Only start DHCPv6 if the RA is new or has changed
* Fixed dhcpcd owning RA addressing and routes if disabled in kernel