i40e: add VEB switching support

i40e: add VEB switching support

VEB switching feature for i40e is used to enable the switching between the
VSIs connect to the virtual bridge. The old implementation is setting the
virtual bridge mode as VEPA which is port aggregation. Enable the switching
ability by setting the loop back mode for the specific VSIs which connect
to PF or VFs.

VEB/VSI/VEPA are concepts not specific to the i40e HW, the concepts are
from 802.1qbg spec
IEEE EVB tutorial:
http://www.ieee802.org/802_tutorials/2009-11/evb-tutorial-draft-20091116_v09.pdf

VEB: a virtual switch can forward the packet based on the specific match
field.
VSI: a virtual interface connect between the VEB/VEPA and virtual machine.
VEPA: a virtual Ethernet port aggregator will upstream the packets from
VSI to the LAN port.

Signed-off-by: Zhe Tao <zhe.tao@intel.com>
Acked-by: Jingjing Wu <jingjing.wu@intel.com>