Update server_functions.sqf

If ***_result = _vNew - _vOld*** then _result is returned 0; (since ex: 20-20 = _result)
That returned value is set to the variable that is sent to the database in server_playerSync.sqf.
So the stats gets update to 0. Should be the new value instead.
Thanks also to infistar for sorting this out with me.
Based on : https://github.com/vbawol/DayZ-Epoch/issues/1268