netfilter: ipset: list:set timeout variant fixes

- the timeout value was actually not set
- the garbage collector was broken

The variant is fixed, the tests to the ipset testsuite are added.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>