netfilter: xt_limit: have r->cost != 0 case work

Commit v2.6.19-rc1~1272^2~41 tells us that r->cost != 0 can happen when
a running state is saved to userspace and then reinstated from there.

Make sure that private xt_limit area is initialized with correct values.
Otherwise, random matchings due to use of uninitialized memory.
Signed-off-by: Jan Engelhardt <jengelh@inai.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/xt_limit.c

@@ -117,11 +117,11 @@ static int limit_mt_check(const struct xt_mtchk_param *par)
 
 	/* For SMP, we only want to use one set of state. */
 	r->master = priv;
-	if (r->cost == 0) {
 	/* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
 	   128. */
 	priv->prev = jiffies;
 	priv->credit = user2credits(r->avg * r->burst); /* Credits full. */
+	if (r->cost == 0) {
 		r->credit_cap = priv->credit; /* Credits full. */
 		r->cost = user2credits(r->avg);
 	}