[X.25]: Adds /proc/sys/net/x25/x25_forward to control forwarding.

echo "1" > /proc/sys/net/x25/x25_forward 
To turn on x25_forwarding, defaults to off
Requires the previous patch.

Signed-off-by: Andrew Hendry <andrew.hendry@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 81480e6..665412c 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -699,7 +699,8 @@
 	NET_X25_CALL_REQUEST_TIMEOUT=2,
 	NET_X25_RESET_REQUEST_TIMEOUT=3,
 	NET_X25_CLEAR_REQUEST_TIMEOUT=4,
-	NET_X25_ACK_HOLD_BACK_TIMEOUT=5
+	NET_X25_ACK_HOLD_BACK_TIMEOUT=5,
+	NET_X25_FORWARD=6
 };
 
 /* /proc/sys/net/token-ring */