flow-hash: Add symmetric flag for flow hashing

When 'Symmetric' flag is enabled, it will sort the addresses
and hence, same flow hash will be calculated on both directions.

Change-Id: I5d846f8d0b94ca1121e03d15b02bb56edb5887b1
Signed-off-by: Mohsin Kazmi <sykazmi@cisco.com>
diff --git a/src/vnet/ip/lookup.h b/src/vnet/ip/lookup.h
index 3740238..4c598e3 100644
--- a/src/vnet/ip/lookup.h
+++ b/src/vnet/ip/lookup.h
@@ -64,6 +64,7 @@
 #define IP_FLOW_HASH_SRC_PORT (1<<3)
 #define IP_FLOW_HASH_DST_PORT (1<<4)
 #define IP_FLOW_HASH_REVERSE_SRC_DST (1<<5)
+#define IP_FLOW_HASH_SYMMETRIC (1<<6)
 
 /** Default: 5-tuple without the "reverse" bit */
 #define IP_FLOW_HASH_DEFAULT (0x1F)
@@ -74,7 +75,8 @@
 _(sport, IP_FLOW_HASH_SRC_PORT)                 \
 _(dport, IP_FLOW_HASH_DST_PORT)                 \
 _(proto, IP_FLOW_HASH_PROTO)	                \
-_(reverse, IP_FLOW_HASH_REVERSE_SRC_DST)
+_(reverse, IP_FLOW_HASH_REVERSE_SRC_DST)	\
+_(symmetric, IP_FLOW_HASH_SYMMETRIC)
 
 /**
  * A flow hash configuration is a mask of the flow hash options