Import dhcpcd-6.5.1 with the following changes:

  *  Don't work on bridge, or ptp interfaces unless explicitly told
  *  Poll for IFF_RUNNING again but avoid constantly sending IFF_UP
     (should now fix all carrier problems on BSD virtual interfaces)
  *  Don't crash when processing IPv6 route calls from the kernel
     when IPv6 resources have been disabled in dhcpcd
  *  Allow the same IP address to be shared across different interfaces
     Interface with the lowest metric gets the IP address, will move
     to the next highest if dropped (interface departs, carrier drops, etc)
  *  Delegated prefix addresses are now reported via DELEGATE6
  *  Work better with unknown delegated prefix lengths
  *  Move IPv4LL and ARP to the DHCP eloop queue to fix timing issues
  *  Add IA PD documentation update from christos