netfilter: ip_tables: fix build error

Fix build error introduced by commit bb70dfa5 (netfilter: xtables:
consolidate comefrom debug cast access):

net/ipv4/netfilter/ip_tables.c: In function 'ipt_do_table':
net/ipv4/netfilter/ip_tables.c:421: error: 'comefrom' undeclared (first use in this function)
net/ipv4/netfilter/ip_tables.c:421: error: (Each undeclared identifier is reported only once
net/ipv4/netfilter/ip_tables.c:421: error: for each function it appears in.)

Signed-off-by: Patrick McHardy <kaber@trash.net>

net/ipv4/netfilter/ip_tables.c

@@ -418,7 +418,7 @@ ipt_do_table(struct sk_buff *skb,
 #endif
 		verdict = t->u.kernel.target->target(skb, &tgpar);
 #ifdef CONFIG_NETFILTER_DEBUG
-		if (comefrom != 0xeeeeeeec && verdict == IPT_CONTINUE) {
+		if (tb_comefrom != 0xeeeeeeec && verdict == IPT_CONTINUE) {
 			printk("Target %s reentered!\n",
 			       t->u.kernel.target->name);
 			verdict = NF_DROP;