Import dhcpcd-6.6.2 with the following changes:
  *  TAILQ macros are now pulled in via config.h only so dhcpcd compiles
     on systems where sys/queue.h does not exist at all.
  *  Remove DHCP state correctly when the interface departs
  *  End the IPv4LL state when DHCP is stopped
  *  Ensure that any DHCP leased offered still exists when assigning an
     IPv4LL address