[NET]: Introducing socket mark socket option.

A userspace program may wish to set the mark for each packets its send
without using the netfilter MARK target. Changing the mark can be used
for mark based routing without netfilter or for packet filtering.

It requires CAP_NET_ADMIN capability.

Signed-off-by: Laszlo Attila Toth <panther@balabit.hu>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/route.h b/include/net/route.h
index 4eabf00..fcc6d5b 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -27,6 +27,7 @@
 #include <net/dst.h>
 #include <net/inetpeer.h>
 #include <net/flow.h>
+#include <net/sock.h>
 #include <linux/in_route.h>
 #include <linux/rtnetlink.h>
 #include <linux/route.h>
@@ -149,6 +150,7 @@
 				   int flags)
 {
 	struct flowi fl = { .oif = oif,
+			    .mark = sk->sk_mark,
 			    .nl_u = { .ip4_u = { .daddr = dst,
 						 .saddr = src,
 						 .tos   = tos } },