[tftp] Remove unnecessary delay when opening a connection

The retry timer is used to retransmit TFTP packets lost on the network,
and to start a new connection.  There is an unnecessary delay while
waiting for name resolution because the timer period is fixed and cannot
be shortened when name resolution completes.  This patch keeps the timer
period at zero while name resolution takes place so that no time is lost
once before sending the first packet.

Reported-by: Thomas Horsten <thomas@horsten.com>
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Marty Connor <mdc@etherboot.org>

src/net/udp/tftp.c

  */
 static int tftp_send_packet ( struct tftp_request *tftp ) {
 
-	/* Update retransmission timer */
+	/* Update retransmission timer.  While name resolution takes place the
+	 * window is zero.  Avoid unnecessary delay after name resolution
+	 * completes by retrying immediately.
+	 */
 	stop_timer ( &tftp->timer );
-	start_timer ( &tftp->timer );
+	if ( xfer_window ( &tftp->socket ) ) {
+		start_timer ( &tftp->timer );
+	} else {
+		start_timer_nodelay ( &tftp->timer );
+	}
 
 	/* Send RRQ or ACK as appropriate */
 	if ( ! tftp->peer.st_family ) {