net: hns3: package new functions to simplify hclgevf_mbx_handler code

This patch packages two new function to simplify the function
hclgevf_mbx_handler, and it can 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>