bridge: Netlink interface fix.

This commit is correcting NETLINK br_fill_ifinfo() to be able to
handle 'filter_mask' with multiple flags asserted.

Fixes: 36a8e8e2

 ("bridge: Extend br_fill_ifinfo to return MPR status")

Signed-off-by: Henrik Bjoernlund <henrik.bjoernlund@microchip.com>
Reviewed-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Suggested-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Tested-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>