Import dhcpcd-6.2.1 with the folowing changes:

 * on BSD only flush RA routers and prefixes when trying to own them.
 * Mark some data locations as read only and fix a build issue.
 * Fix some possible NULL dereferences, CID 1153963.
 * Fix CID: 1153964 and 1153966
 * Add support for RFC3495 DHCP option for CableLabs Clients.
   Note that for the TSP suboption 3 we only support the FQDN encoding.
 * Init system detection moved to dhcpcd-run-hooks(8)
 * Fix compile errors and warnings with IPv6 disabled.