connmark requires ip_conntrack

Hi Patrick,

The connmark match/target require ip_conntrack to work. This patch add such dependency via need_ip_conntrack(). Thanks to Piotr Chytla for spotting this problem.

index 1346380..05d66ab 100644
@@ -109,6 +109,7 @@ static struct ipt_target ipt_connmark_re
 
 static int __init init(void)
 {
+	need_ip_conntrack();
 	return ipt_register_target(&ipt_connmark_reg);
 }
 

index bf8de47..d99cf71 100644
@@ -76,6 +76,7 @@ static struct ipt_match connmark_match =
 
 static int __init init(void)
 {
+	need_ip_conntrack();
 	return ipt_register_match(&connmark_match);
 }
 

For the CONNMARK target it makes sense. As for matches, I don't really like loading modules where semantically something else (like assuming 0) would also make sense, but I've applied the patch for consistency reasons with other matches. Thanks.