cache: honor -c/--check for reset commands

cache: honor -c/--check for reset commands

Currently:

  nft -c reset rules ip x

ignores -c/--check.

The reset and list commands use the netlink GET/DUMP nfnetlink API which
provides no check semantics, compared to the NEW/DELETE nfnetlink batch
API which indeed does.

Emulate -c/--check for the reset command by handling this as a list
command, so the state of the objects is just listed, not reset. This
allows to check for presence and dump the content of the objects.

Fixes: dbff26bfba83 ("cache: consolidate reset command")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>