vdpa/mlx5: Add RX counters to debugfs

For each interface, either VLAN tagged or untagged, add two hardware
counters: one for unicast and another for multicast. The counters count
RX packets and bytes and can be read through debugfs:

$ cat /sys/kernel/debug/mlx5/mlx5_core.sf.1/vdpa-0/rx/untagged/mcast/packets
$ cat /sys/kernel/debug/mlx5/mlx5_core.sf.1/vdpa-0/rx/untagged/ucast/bytes

This feature is controlled via the config option
MLX5_VDPA_STEERING_DEBUG. It is off by default as it may have some
impact on performance.

includes a fixup By Yang Yingliang <yangyingliang@huawei.com>:

vdpa/mlx5: fix check wrong pointer in mlx5_vdpa_add_mac_vlan_rules()

The local variable 'rule' is not used anymore, fix return value
check after calling mlx5_add_flow_rules().

Signed-off-by: Eli Cohen <elic@nvidia.com>
Message-Id: <20221114131759.57883-9-elic@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Message-Id: <20230104074418.1737510-1-yangyingliang@huawei.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Eli Cohen <elic@nvidia.com>
Acked-by: Jason Wang <jasowang@redhat.com>