netfilter: nf_tables: audit log object reset once per table

When resetting multiple objects at once (via dump request), emit a log
message per table (or filled skb) and resurrect the 'entries' parameter
to contain the number of objects being logged for.

To test the skb exhaustion path, perform some bulk counter and quota
adds in the kselftest.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Acked-by: Paul Moore <paul@paul-moore.com> (Audit)
Signed-off-by: Florian Westphal <fw@strlen.de>