smbd: some write time fixes

smbd: some write time fixes

- only the first non truncating write causes
  the write time update with 2 seconds delay.
  It's not enough to check for an existing update event
  as it will be NULL after the event was triggered.

- SMBwrite truncates always update the write time
  unless the sticky write time is set.

- SMBwrite truncates don't trigger a write time update on close.

metze
(cherry picked from commit be8ac33179f56296118435e2732ccffdf7ddd305)