Fix bug: sometimes valid entries in hash:* types of sets were evicted

Wrong index was used and therefore when shrinking a hash bucket at
deleting an entry, valid entries could be evicted as well.
Thanks to Eric Ewanco for the thorough bugreport.

Fixes netfilter bugzilla #1119

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