ip6tables: masquerade: use fully-random so that nft can understand the rule

ip6tables: masquerade: use fully-random so that nft can understand the rule

Here is the problem:

[]# nft -v
nftables v0.9.8 (E.D.S.)
[]# iptables-nft -v
iptables v1.8.7 (nf_tables): no command specified
Try `iptables -h' or 'iptables --help' for more information.
[]# nft flush ruleset
[]# ip6tables-nft -t nat -A POSTROUTING  -j MASQUERADE --random-full
[]# nft list ruleset
table ip6 nat {
	chain POSTROUTING {
		type nat hook postrouting priority srcnat; policy accept;
		counter packets 0 bytes 0 masquerade  random-fully
	}
}
[]# nft list ruleset > /tmp/ruleset
[]# nft flush ruleset
[]# nft -f /tmp/ruleset
/tmp/ruleset:4:54-54: Error: syntax error, unexpected newline
		counter packets 0 bytes 0 masquerade  random-fully

That's because nft list ruleset saves "random-fully" which is wrong
format for nft -f, right should be "fully-random".

We face this problem because we run k8s in Virtuozzo container, and k8s
creates those "random-fully" rules by iptables(nft) and then CRIU can't
restore those rules using nft.

Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Signed-off-by: Florian Westphal <fw@strlen.de>