netfilter: hashlimit: byte-based limit mode

can be used e.g. for ingress traffic policing or
to detect when a host/port consumes more bandwidth than expected.

This is done by optionally making cost to mean
"cost per 16-byte-chunk-of-data" instead of "cost per packet".

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/netfilter/xt_hashlimit.h

@@ -6,7 +6,11 @@
 /* timings are in milliseconds. */
 #define XT_HASHLIMIT_SCALE 10000
 /* 1/10,000 sec period => max of 10,000/sec.  Min rate is then 429490
-   seconds, or one every 59 hours. */
+ * seconds, or one packet every 59 hours.
+ */
+
+/* packet length accounting is done in 16-byte steps */
+#define XT_HASHLIMIT_BYTE_SHIFT 4
 
 /* details of this structure hidden by the implementation */
 struct xt_hashlimit_htable;
@@ -17,6 +21,10 @@ enum {
 	XT_HASHLIMIT_HASH_SIP = 1 << 2,
 	XT_HASHLIMIT_HASH_SPT = 1 << 3,
 	XT_HASHLIMIT_INVERT   = 1 << 4,
+	XT_HASHLIMIT_BYTES    = 1 << 5,
+#ifdef __KERNEL__
+	XT_HASHLIMIT_MAX      = 1 << 6,
+#endif
 };
 
 struct hashlimit_cfg {