net: hns3: remove mailbox and reset work in hclge_main

There are three work (mbx_service_task, service_task,
rst_service_task) in the HNS3 driver, mbx_service_task is for
handling mailbox work, service_task is for periodic management
issue and rst_service_task is for reset related issue, which can
be handled in a single work.

This patch removes the mbx_service_task and rst_service_task
work, and moves the related handling to the service_task work
in order to remove concurrency between the three work and to
improve efficiency.

BTW, since stats_timer in struct hclge_hw_stats is not needed
anymore, so removes the definition of struct hclge_hw_stats,
and moves mac_stats into struct hclge_dev.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>