net: hns3: fix change RSS 'hfunc' ineffective issue

When user change rss 'hfunc' without set rss 'hkey' by ethtool
-X command, the driver will ignore the 'hfunc' for the hkey is
NULL. It's unreasonable. So fix it.

Fixes: 46a3df9f ("net: hns3: Add HNS3 Acceleration Engine & Compatibility Layer Support")
Fixes: 374ad291

 ("net: hns3: Add RSS general configuration support for VF")
Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>