net: hns3: use a reserved byte to identify need_resp flag

This patch uses a reserved byte in the hclge_mbx_vf_to_pf_cmd
to save the need_resp flag, so when PF received the mailbox,
it can use it to decise whether send a response to VF.

For hclge_set_vf_uc_mac_addr(), it should use mbx_need_resp flag
to decide whether send response to VF.

Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>