net/bridge: Add 'hairpin' port forwarding mode

This patch adds a 'hairpin' (also called 'reflective relay') mode
port configuration to the Linux Ethernet bridge kernel module.
A bridge supporting hairpin forwarding mode can send frames back
out through the port the frame was received on.

Hairpin mode is required to support basic VEPA (Virtual
Ethernet Port Aggregator) capabilities.

You can find additional information on VEPA here:
http://tech.groups.yahoo.com/group/evb/
http://www.ieee802.org/1/files/public/docs2009/new-hudson-vepa_seminar-20090514d.pdf
http://www.internet2.edu/presentations/jt2009jul/20090719-congdon.pdf

An additional patch 'bridge-utils: Add 'hairpin' port forwarding mode'
is provided to allow configuring hairpin mode from userspace tools.

Signed-off-by: Paul Congdon <paul.congdon@hp.com>
Signed-off-by: Anna Fischer <anna.fischer@hp.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index d5b5537..8319247 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -81,6 +81,9 @@
 	struct timer_list		message_age_timer;
 	struct kobject			kobj;
 	struct rcu_head			rcu;
+
+	unsigned long 			flags;
+#define BR_HAIRPIN_MODE		0x00000001
 };
 
 struct net_bridge