igc: Remove igc_nfc_rule_exit()

During igc_down(), we call igc_nfc_rule_exit() which traverse the NFC
rule list disabling filters one by one. Later on in igc_down() flow
we issue an hardware reset which also clear all filters.  Since we
already reset the hardware, we don't actually need to disable each
filter manually. In order to simplify the code, this patch removes
igc_nfc_rule() altogether.

Signed-off-by: Andre Guedes <andre.guedes@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>