nft-ruleparse: parse meta mark set as MARK target

nft-ruleparse: parse meta mark set as MARK target

Mixing nftables and iptables-nft in the same table doesn't work,
but some people do this.

v1.8.8 ignored rules it could not represent in iptables syntax,
v1.8.9 bails in this case.

Add parsing of meta mark expressions so iptables-nft can render them
as -j MARK rules.

This is flawed, nft has features that have no corresponding
syntax in iptables, but we can't undo this.

Link: https://bugzilla.netfilter.org/show_bug.cgi?id=1659
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Phil Sutter <phil@nwl.cc>