libnftables set element printing, DATA_CHAIN

[Patrick McHardy <kaber@trash.net>]

[resending because of incorrect list address]

I was looking at some incorrect output in netlink debugging for set elements
and noticed a few things that seem odd:

First, the regular netlink debugging seems very incomplete, it doesn't
print verdict types, it prints [end] whether the set contains intervals
and the set is an interval end or not and its messing up the output.

Next I'm wondering about what DATA_CHAIN is supposed to be. I guess its
the chain for a jump or goto verdict, This is even encoded in the
XML and JSON output. This seems wrong to me, there is no DATA_CHAIN,
there are JUMP or GOTO verdicts that include a chain. The specific
verdict is also missing, so its not possible to distinguish these
two cases.

I could fix up the debugging output, but this looks like someone more
familiar with the XML and JSON stuff should have a look at this and
fix all of this consistently before we release it as wire format.