igc: Remove IGC_MAC_STATE_SRC_ADDR flag

MAC address filters based on source address are not currently supported
by the IGC driver. Despite of that, the driver have some dangling code
to handle it, inherited from IGB driver. This patch removes that code to
prepare for a follow up patch that adds proper source MAC address filter
support.

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>