dhcpv6: do not overwrite config in override for #2633
dhcpv6: do not overwrite config in override for #2633

This provides a manual override track interface to be
enabled or disabled in dhcpv6 as we do not meddle with
the enable flag anymore.  It's not super-useful but it
makes sense to follow the enabled flag in this case.

Suggested by: @marjohn56

opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core