net: RTA_MARK addition

Add a new rt attribute, RTA_MARK, and use it in
rt_fill_info()/inet_rtm_getroute() to support following commands :

ip route get 192.168.20.110 mark NUMBER
ip route get 192.168.20.108 from 192.168.20.110 iif eth1 mark NUMBER
ip route list cache [192.168.20.110] mark NUMBER

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index fbc8cb0..58d4449 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -282,6 +282,7 @@
 	RTA_SESSION, /* no longer used */
 	RTA_MP_ALGO, /* no longer used */
 	RTA_TABLE,
+	RTA_MARK,
 	__RTA_MAX
 };