subnet: dhcp: only accept single ips and normalize them

subnet: dhcp: only accept single ips and normalize them

Net::IP accepts a myriad of different IP objects from ranges to
prefixes to singular IPs. We check if the object consists only of a
singular IP and normalize the IP if it has size 1 (since then it
could still be a /32 prefix or a range consisting of one IP).
Otherwise we would theoretically accept any valid Net::IP object here.

Signed-off-by: Stefan Hanreich <s.hanreich@proxmox.com>
Tested-by: Hannes Duerr <h.duerr@proxmox.com>
Link: https://lore.proxmox.com/20250307125056.169575-3-s.hanreich@proxmox.com
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>