bridge: netlink: account for IFLA_BRPORT_{B, M}CAST_FLOOD size and policy

The attribute sizes for IFLA_BRPORT_MCAST_FLOOD and
IFLA_BRPORT_BCAST_FLOOD weren't accounted for in br_port_info_size()
when they were added. Do so now and also add the corresponding policy
entries:

Cc: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Cc: Mike Manning <mmanning@brocade.com>
Fixes: b6cb5ac8 ("net: bridge: add per-port multicast flood flag")
Fixes: 99f906e9

 ("bridge: add per-port broadcast flood flag")
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>