net: hns3: refactor function hclge_set_channels()

Currently  hclge_set_channels() is a bit long. Refactor it by extracting
sub process to improve the readability.

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>