net: bridge: teach ndo_dflt_bridge_getlink() more brport flags

This enables ndo_dflt_bridge_getlink() to report a bridge port's
offload settings for multicast and broadcast flooding.

CC: Roopa Prabhu <roopa@cumulusnetworks.com>
CC: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>