sctp: Store a flowi in transports to provide persistent keying.

Several future simplifications are possible now because of this.

For example, the sctp_addr unions can simply refer directly to
the flowi information.

Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sctp/structs.h

@@ -894,6 +894,7 @@ struct sctp_transport {
 		/* Is this structure kfree()able? */
 		malloced:1;
 
+	struct flowi fl;
 
 	/* This is the peer's IP address and port. */
 	union sctp_addr ipaddr;