Minor correction in ARM for reservation mode correlation

In the correspondence list between old and new reservation modes[1], there are some of the old ones that correspond to setting only to SOME and not to ALL of the new ones. One example is "disabled".

disabled:

"Dhcp6": {
    "reservations-global": false,
    "reservations-in-subnet": false
}

On a Kea with an empty config, setting that reservation mode with "remote-subnet6-set" and then doing a "config-get" returns only those two values and leaves out "reservations-out-of-pool".

And now here is the correspondece for "global".

global:

"Dhcp6": {
    "reservations-global": true,
    "reservations-in-subnet": false,
    "reservations-out-of-pool": false
}

Doing the same experiment for "global" returns only

{
    "reservations-global": true,
    "reservations-in-subnet": false
}

leaving out "reservations-out-of-pool". I think this is the correct behavior. More generally, the rule is whenever "reservations-in-subnet" is false, "reservations-out-of-pool" should not be taken into account.

What I think needs be done is to remove "reservations-out-of-pool": false from the global correlation in the ARM.

Same for v4.

Tested with forge tests test_remote_subnet[46]_set_reservation_mode_global(|_old).

[1] https://kea.readthedocs.io/en/latest/arm/dhcp6-srv.html#reservations6-tuning