privsep: default to using _dhcpcd and not _dhcp
privsep: default to using _dhcpcd and not _dhcp

_dhcp home dir defaults to /var/empty.
System integrators can and should be in charge of changing it when needed.
Packagers on the other hand don't have such a luxury and so should not
use _dhcp by default.

rsmarples/dhcpcd,rsmarples/dhcpcd,rsmarples/dhcpcd