debug: include kernel set information on cache fill

debug: include kernel set information on cache fill

Honor --debug=netlink flag also when doing initial set dump
from the kernel.

With recent libnftnl update this will include the chosen
set backend name that is used by the kernel.

Because set names are scoped by table and protocol family,
also include the family protocol number.

Dumping this information breaks tests/py as the recorded
debug output no longer matches, this is fixed in previous
change.

Signed-off-by: Florian Westphal <fw@strlen.de>