igc: Enable HW VLAN Insertion and HW VLAN Stripping

Add HW VLAN acceleration protocol handling. In case of HW VLAN tagging,
we need that protocol available in the ndo_start_xmit(), so that it will be
stored in a new fields in the skb.

HW offloading is set to OFF by default.
Users are allow to turn on/off Rx/Tx HW VLAN acceleration via ethtool.

Signed-off-by: Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@intel.com>
Tested-by: Dvora Fuxbrumer <dvorax.fuxbrumer@linux.intel.com>
Acked-by: Sasha Neftin <sasha.neftin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>