ethtool: Don't flush n-tuple list from ethtool_reset()

The n-tuple list should be flushed if and only if the ETH_RESET_FILTER
flag is set and the driver is able to reset filtering/flow direction
hardware without also resetting a component whose flag is not set.
This test is best left to the driver.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>