network: get_local_ip_from_cidr: return unique IPs

network: get_local_ip_from_cidr: return unique IPs

to avoid erroring out when "multiple" addresses are configured on live
migration, when in fact it's the same IP multiple times.

Seems like the same problem for a caller in pve-cluster was fixed by checking
the uniqueness afterwards, see commit 266041169beb36c8892ca54265e2d91335307ffb
in pve-cluster. But there doesn't seem to be any caller relying on the current
behavior, and no additional information other than the addresses are returned,
so fix it here.

Reported here:
https://forum.proxmox.com/threads/live-migration-of-vms-via-full-mesh-network-could-not-get-ip-multiple-addresses-configured-on-local-node-for-network.84585/

Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>