igc: Fix NFC rules leak when driver is unloaded

If we have RFC rules in adapter->nfc_rule_list when the IGC driver
is unloaded, all rules are leaked. This patch fixes the issue by
introducing the helper igc_flush_nfc_rules() and calling it in
igc_remove(). It also updates igc_set_features() so is reuses the
new helper instead of re-implementing it.

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>