subnet: dhcp: do not allow overlapping dhcp ranges

subnet: dhcp: do not allow overlapping dhcp ranges

Check for overlapping DHCP ranges and reject them if there are any
overlaps. If we can be certain that there are no overlapping DHCP
ranges this saves us from running into errors later in IPAM modules
where overlapping DHCP ranges are not allowed.

Signed-off-by: Stefan Hanreich <s.hanreich@proxmox.com>
Tested-by: Hannes Duerr <h.duerr@proxmox.com>
Link: https://lore.proxmox.com/20250307125056.169575-4-s.hanreich@proxmox.com
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>