rocker: remove swdev mode

Remove use of 'swdev' mode in rocker. rocker dev offloads
can use the BRIDGE_FLAGS_SELF to indicate offload to hardware.

Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>