igc: Remove mac_table from igc_adapter

In igc_adapter we keep a sort of shadow copy of RAL and RAH registers.
There is not much benefit in keeping it, at the cost of maintainability,
since adding/removing MAC address filters is not hot path, and we
already keep filters information in adapter->nfc_filter_list for cleanup
and restoration purposes.

So in order to simplify the MAC address filtering code and prepare it
for source address support, this patch removes the mac_table from
igc_adapter.

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>