DHCP6: Revert part of prior - only allow vendorclassid to disable
DHCP6: Revert part of prior - only allow vendorclassid to disable

Not set.
dhcpcd owns the IANA_PEN defined.
Either use it as is, or get your own.
This restores the prior behaviour but still allows the option
as a whole to be disabled by vendorclassid being disabled.

rsmarples/dhcpcd,rsmarples/dhcpcd,rsmarples/dhcpcd