radius: kea sometimes selects its own IP address instead of serving the one returned by Radius

In case of such configuration:

 "shared-networks": [{
            "name": "net-1",
            "subnet4": [{
                "subnet": "192.168.50.0/24",
                "interface": "$(SERVER_IFACE)",
                "pools": [{
                    # gold
                    "pool": "192.168.50.5 - 192.168.50.5",
                    "client-class": "gold"
                }]
            }, {
                "subnet": "192.168.60.0/24",
                "interface": "$(SERVER_IFACE)",
                "pools": [{
                    # silver
                    "pool": "192.168.60.6 - 192.168.60.6",
                    "client-class": "silver"
                }]
            }, {
                "subnet": "192.168.70.0/24",
                "interface": "$(SERVER_IFACE)",
                "client-class": "platinum",  # platinum
                "pools": [{
                    "pool": "192.168.70.5 - 192.168.70.5"
                }]
            }]
        }]

with authorize file in Radius:

11:08:00:27:b0:c1:42    Cleartext-password := "08:00:27:b0:c1:42"
    Framed-IP-Address = "192.168.52.52",
    Framed-Pool = "gold"

for this request:

DISCOVER: chaddr="08:00:27:b0:c1:42", client_id="11080027b0c142"

Kea returns 192.168.50.5 instead of 192.168.52.52

To replicate the issue run test tests/dhcpv4/kea_only/radius/test_radius.py::test_select_from_radius_and_ignore_complex_subnets_with_classes

from this change: forge!36 (merged)