Log Message:
Import dhcpcd-10.0.6 with the following changes:

 * privsep: Stop proxying stderr to console and fix some detachment issues
 * non-privsep: Fix launcher hangup
 * DHCP6: Allow the invalid interface name - to mean don't assign an address \ 
from a delegated prefix
 * DHCP6: Load the configuration for the interface being activated from prefix \ 
delegation