netfilter: xt_recent: fix regression in rules using a zero hit_count

Commit 8ccb92ad

 (netfilter: xt_recent: fix false match) fixed supposedly
false matches in rules using a zero hit_count. As it turns out there is
nothing false about these matches and people are actually using entries
with a hit_count of zero to make rules dependant on addresses inserted
manually through /proc.

Since this slipped past the eyes of three reviewers, instead of
reverting the commit in question, this patch explicitly checks
for a hit_count of zero to make the intentions more clear.

Reported-by: Thomas Jarosch <thomas.jarosch@intra2net.com>
Tested-by: Thomas Jarosch <thomas.jarosch@intra2net.com>
Cc: stable@kernel.org
Signed-off-by: Patrick McHardy <kaber@trash.net>