Added code to ensure that, even if there is a constant stream of SMB

Added code to ensure that, even if there is a constant stream of SMB
requests with no echos or pauses, that timeout processing is still
done at SELECT_TIMOUT intervals.

This is done by updating a counter of the number of SMB's processed,
and checking if the time has come for timeout processing every 200
SMB requests.

This should fix the 'smbd is not responding to a HUP signal' that
someone submitted a (rather complex) patch for.
Jeremy.