Most of the interface statistics in "show interface" are MAC level (hardware) statistics and cannot be reset except by rebooting the sensor.
The higher level statistics, such as "show statistics virtual-sensor" can be reset by appending the keyword "clear" to the request. In that case, the current statistics are displayed and then reset internally. The next invocation will show statistics since the "clear". One of the statistics is "Seconds since last reset" and you can use it to verify that your reset is taking place.
