i40e: Fix a bug in ethtool for FD drop packet filter action

A drop action comes down as a ring_cookie value, so allow it as
a special value that can be used to configure destination control.

Also fix the output to filter read command accordingly.

Change-ID: I9956723cee42f3194885403317dd21ed4a151144
Signed-off-by: Anjali Singhai Jain <anjali.singhai@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>