net: hns3: fix pfc packet number incorrect after querying pfc parameters

Currently, driver will send command to firmware to query pfc packet number
when user uses dcb tool to get pfc parameters. However, the periodic
service task will also periodically query and record MAC statistics,
including pfc packet number.

As the hardware registers of statistics is cleared after reading, it will
cause pfc packet number of MAC statistics are not correct after using dcb
tool to get pfc parameters.

To fix this problem, when user uses dcb tool to get pfc parameters, driver
updates MAC statistics firstly and then get pfc packet number from MAC
statistics.

Fixes: 64fd2300 ("net: hns3: add support for querying pfc puase packets statistic")
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>