net: hns3: add a check before PF inform VF to reset

When setting VF's MAC from PF, if the VF driver not loaded, the
firmware will return error to PF.

So PF should check whether VF is alive before sending message to
VF when setting VF's MAC.

Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>