Log Message:
Import dhcpcd-8.0.5 with the following changes:

*  inet6: Fix default route not being installed
*  DHCP: If root fs is network mounted, enable last lease extend
*  man: Fix lint errors.
*  BSD: avoid RTF_WASCLONED routes
*  DHCP: Give a better message when packet validation fails
*  DHCP: Ensure we have enough data to checksum IP and UDP

The last change fixes a potential DoS attack introduced in dhcpcd-8.0.3 when
the checksuming code was changed to accomodate variable length IP headers.