partial fix #5496: ipam: netbox: properly return allocated ip

partial fix #5496: ipam: netbox: properly return allocated ip

The netbox integration did not properly return the IP when creating
the entries in netbox. This lead to errors on starting the guest,
stating that an IP could not be allocated.

Originally-by: lou lecrivain <lou.lecrivain@wdz.de>
Signed-off-by: Stefan Hanreich <s.hanreich@proxmox.com>
Tested-by: Hannes Duerr <h.duerr@proxmox.com>
Link: https://lore.proxmox.com/20250310085103.30549-6-s.hanreich@proxmox.com
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>