i40e: Add debugfs hooks to print current total FD filter count

"fd current cnt" can be used to print the total filters consumed
by this interface, this includes guaranteed and best effort filters.

Change-ID: I2c417810c4999ce1388d2ea26f8e69679ba33966
Signed-off-by: Anjali Singhai Jain <anjali.singhai@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>