This has two advantages:

- Update the scoreboard in a single call making xfer_done and elasped_time come
  from the same moment and reducing scoreboard update overhead
- During FTP uploads the number of received bytes also get updated in XFER_DONE
  making ftpwho -o json display "transfer_bytes" for uploads as well

Signed-off-by: Marton Balint <cus@passwd.hu>

This commit removes the previously used blocksize or filesize percentage based
scoreboard updates and starts using elapsed time based scoreboard updates.

Percent based scoreboard updates could have been too infrequent for big files
and slow link speeds, blocksize based scoreboard updates could have been too
frequent for fast links.

Also this changes the meaning of PR_TUNABLE_XFER_SCOREBOARD_UPDATES, previously
it meant the number of transferred blocks to wait until a scoreboard update
happened, now it means the number of deciseconds to wait between subsequent
scoreboard updates.

Deciseconds as the unit were chosen so the default of
PR_TUNABLE_XFER_SCOREBOARD_UPDATES of 10 is unchanged and will mean a
scoreboard update every second.