net/hns3: fix insecure way to query MAC statistics

net/hns3: fix insecure way to query MAC statistics

The query way of MAC statistics in HNS3 PF driver is as following:
1) get MAC statistics register number and calculate descriptor number.
2) use above descriptor number to send command to firmware to query all
   MAC statistics and copy to hns3_mac_stats struct in driver.

The preceding way does not verify the validity of the number of obtained
register, which may cause memory out-of-bounds.

Fixes: 8839c5e202f3 ("net/hns3: support device stats")
Cc: stable@dpdk.org
Signed-off-by: Huisong Li <lihuisong@huawei.com>
Signed-off-by: Min Hu (Connor) <humin29@huawei.com>