netfilter: ipset: List timing out entries with "timeout 1" instead of zero

When listing sets with timeout support, there's a probability that
just timing out entries with "0" timeout value is listed/saved.
However when restoring the saved list, the zero timeout value means
permanent elelements.

The new behaviour is that timing out entries are listed with "timeout 1"
instead of zero.

Fixes netfilter bugzilla #1258.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>