Firewall Ruleset should respect node cidr instead of hardcoded 10.0.0.0/8

[majst01]

Description

Part of: metal-stack/releases#324

the nftables ruleset actually defines the cluster_prefixes like so:

# Prefixes in the cluster, typically 10.x.x.x
	# FIXME Should be filled with nodeCidr
	set cluster_prefixes {
		type ipv4_addr
		flags interval
		auto-merge
		elements = { 10.0.0.0/8 }
	}

This should be filled with the nodeCidrs as stated in the FIXME

Also it should be made IPv6 compatible as well