And update most of the comments to refer to "nftables" rather than
"iptables" (even though it doesn't actually do any nftables updating
at this point).
For now the proxy also internally creates a
utiliptablestesting.FakeIPTables to keep the existing sync code
compiling.
(It is confusing, but allowed, to have distinct "KUBE-SERVICES" chains
in "nat" and "filter" in iptables, but in nftables the "type nat" and
"type filter" chains end up in the same table, so we'll need different
names for the two.)
Change the svcPortInfo and endpointInfo fields to string rather than
utiliptables.Chain, and various fixups from there.
Also use a proper set for activeNATChains, and fix the capitalization
of endpointInfo.chainName.
