netlink: Show the handles of unknown rules in "nft monitor trace"

netlink: Show the handles of unknown rules in "nft monitor trace"

When "nft monitor trace" doesn't know a rule (because it was only added
to the ruleset after nft was invoked), that rule is silently omitted in
the trace output, which can come as a surprise when debugging issues.

Instead, we can at least show the information we got via netlink, i.e.
the family, table and chain name, rule handle and verdict.

Signed-off-by: Luis Ressel <aranea@aixah.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>