Support port MDB and bridge flag operations.

As the hardware can manage multicast forwarding itself, offload_fwd_mark
can be unconditionally set to true.
Signed-off-by: NDENG Qingfang <dqfext@gmail.com>
Reviewed-by: NVladimir Oltean <olteanv@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>