Current hwmode settings are "vepa" or "veb".  These are for NIC interfaces
with basic bridging function offloaded to HW.  Add new "swdev" for full
switch device offloads.
Signed-off-by: NScott Feldman <sfeldma@gmail.com>
Signed-off-by: NJiri Pirko <jiri@resnulli.us>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>