route: Add multipath_hash in flowi_common to make user-define hash

Current fib_multipath_hash_policy can make hash based on the L3 or
L4. But it only work on the outer IP. So a specific tunnel always
has the same hash value. But a specific tunnel may contain so many
inner connections.

This patch provide a generic multipath_hash in floi_common. It can
make a user-define hash which can mix with L3 or L4 hash.

Signed-off-by: wenxu <wenxu@ucloud.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/flow.h b/include/net/flow.h
index 93f2c9a..a50fb77 100644
--- a/include/net/flow.h
+++ b/include/net/flow.h
@@ -40,6 +40,7 @@ struct flowi_common {
 	__u32	flowic_secid;
 	kuid_t  flowic_uid;
 	struct flowi_tunnel flowic_tun_key;
+	__u32		flowic_multipath_hash;
 };
 
 union flowi_uli {
@@ -78,6 +79,7 @@ struct flowi4 {
 #define flowi4_secid		__fl_common.flowic_secid
 #define flowi4_tun_key		__fl_common.flowic_tun_key
 #define flowi4_uid		__fl_common.flowic_uid
+#define flowi4_multipath_hash	__fl_common.flowic_multipath_hash
 
 	/* (saddr,daddr) must be grouped, same order as in IP header */
 	__be32			saddr;