net: hns3: Fix desc num set to default when setting channel

When user set the channel num using "ethtool -L ethX", the desc num
of BD will set to default value, which will cause desc num set by
user lost problem.

This patch fixes it by restoring the desc num set by user when setting
channel num.

Fixes: 09f2af64 ("net: hns3: add support to modify tqps number")
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>