flow, tcp: Move TCP connection table to unified flow table

We want to generalise "connection" tracking to things other than true TCP
connections.  Continue implenenting this by renaming the TCP connection
table to the "flow table" and moving it to flow.c.  The definitions are
split between flow.h and flow_table.h - we need this separation to avoid
circular dependencies: the definitions in flow.h will be needed by many
headers using the flow mechanism, but flow_table.h needs all those protocol
specific headers in order to define the full flow table entry.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

flow.h

@@ -33,4 +33,12 @@ struct flow_common {
 	uint8_t		type;
 };
 
+#define FLOW_INDEX_BITS		17	/* 128k - 1 */
+#define FLOW_MAX		MAX_FROM_BITS(FLOW_INDEX_BITS)
+
+#define FLOW_TABLE_PRESSURE		30	/* % of FLOW_MAX */
+#define FLOW_FILE_PRESSURE		30	/* % of c->nofile */
+
+union flow;
+
 #endif /* FLOW_H */