netfilter: xt_recent: add address masking option

The mask option allows you put all address belonging that mask into
the same recent slot. This can be useful in case that recent is used
to detect attacks from the same network segment.

Tested for backward compatibility.

Signed-off-by: Denys Fedoryshchenko <denys@visp.net.lb>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
index ff9c84c..4541f33 100644
--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -94,6 +94,16 @@
 	       a1->all[3] == a2->all[3];
 }
 
+static inline void nf_inet_addr_mask(const union nf_inet_addr *a1,
+				     union nf_inet_addr *result,
+				     const union nf_inet_addr *mask)
+{
+	result->all[0] = a1->all[0] & mask->all[0];
+	result->all[1] = a1->all[1] & mask->all[1];
+	result->all[2] = a1->all[2] & mask->all[2];
+	result->all[3] = a1->all[3] & mask->all[3];
+}
+
 extern void netfilter_init(void);
 
 /* Largest hook number + 1 */