net: hns3: debugfs add drop packet statistics of multicast and broadcast for igu

Currently, there is no way to get drop packet number of multicast and
broadcast in IGU hardware module, it is not convenient to find problem
when multicast packet or broadcast packet is dropped in IGU, so this
patch adds statistics for them in debugfs.

Signed-off-by: Jie Wang <wangjie125@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>