net: hns3: add result checking for VF when modify unicast mac address

VF changes unicast mac address by sending mailbox msg to PF, then PF
completes the mac address modification. It may fail when the target
uc mac address is already in the mac_vlan table. VF should be aware
of it by reading the message result.

Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>