[NETFILTER]: x_tables: add rateest match

Add rate estimator match. The rate estimator match can match on
estimated rates by the RATEEST target. It supports matching on
absolute bps/pps values, comparing two rate estimators and matching
on the difference between two rate estimators.

This is what I use to route outgoing data connections from a FTP
server over two lines based on the  available bandwidth:

# estimate outgoing rates
iptables -t mangle -A POSTROUTING -o eth0 -j RATEEST --rateest-name eth0 \
                                                     --rateest-interval 250ms \
                                                     --rateest-ewma 0.5s
iptables -t mangle -A POSTROUTING -o ppp0 -j RATEEST --rateest-name ppp0 \
                                                     --rateest-interval 250ms \
                                                     --rateest-ewma 0.5s

# mark based on available bandwidth
iptables -t mangle -A BALANCE -m state --state NEW \
                              -m helper --helper ftp \
                              -m rateest --rateest-delta \
                                         --rateest1 eth0 \
                                         --rateest-bps1 2.5mbit \
                                         --rateest-gt \
                                         --rateest2 ppp0 \
                                         --rateest-bps2 2mbit \
                              -j CONNMARK --set-mark 0x1

iptables -t mangle -A BALANCE -m state --state NEW \
                              -m helper --helper ftp \
                              -m rateest --rateest-delta \
                                         --rateest1 ppp0 \
                                         --rateest-bps1 2mbit \
                                         --rateest-gt \
                                         --rateest2 eth0 \
                                         --rateest-bps2 2.5mbit \
                              -j CONNMARK --set-mark 0x2

iptables -t mangle -A BALANCE -j CONNMARK --restore-mark

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 22d1f10..4182393 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -631,6 +631,16 @@
 	  If you want to compile it as a module, say M here and read
 	  <file:Documentation/kbuild/modules.txt>.  If unsure, say `N'.
 
+config NETFILTER_XT_MATCH_RATEEST
+	tristate '"rateest" match support'
+	depends on NETFILTER_XTABLES
+	select NETFILTER_XT_TARGET_RATEEST
+	help
+	  This option adds a `rateest' match, which allows to match on the
+	  rate estimated by the RATEEST target.
+
+	  To compile it as a module, choose M here.  If unsure, say N.
+
 config NETFILTER_XT_MATCH_REALM
 	tristate  '"realm" match support'
 	depends on NETFILTER_XTABLES