net: hns3: reconstruct function hns3_self_test

This patch reconstructs function hns3_self_test to reduce the code
cycle complexity and make code more concise.

Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>