[tcp] Randomise local TCP port

Signed-off-by: Guo-Fu Tseng <cooldavid@cooldavid.org>
Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/tcp.c

  */
 static int tcp_bind ( struct tcp_connection *tcp, unsigned int port ) {
 	struct tcp_connection *existing;
-	static uint16_t try_port = 1023;
+	uint16_t try_port;
+	unsigned int i;
 
-	/* If no port specified, find the first available port */
+	/* If no port is specified, find an available port */
 	if ( ! port ) {
-		while ( try_port ) {
+		try_port = random();
+		for ( i = 0 ; i < 65536 ; i++ ) {
 			try_port++;
 			if ( try_port < 1024 )
 				continue;