bridge: offload bridge port attributes to switch asic if feature flag set

This patch adds support to set/del bridge port attributes in hardware from
the bridge driver.

With this, when the user sends a bridge setlink message with no flags or
master flags set,
   - the bridge driver ndo_bridge_setlink handler sets settings in the kernel
   - calls the swicthdev api to propagate the attrs to the switchdev
	hardware

   You can still use the self flag to go to the switch hw or switch port
   driver directly.

With this, it also makes sure a notification goes out only after the
attributes are set both in the kernel and hw.

The patch calls switchdev api only if BRIDGE_FLAGS_SELF is not set.
This is because the offload cases with BRIDGE_FLAGS_SELF are handled in
the caller (in rtnetlink.c).

Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>