net: hns3: remove unnecessary MAC enable in app loopback

Packets will not pass through MAC during app loopback.
Therefore, it is meaningless to enable MAC while doing
app loopback. This patch removes this unnecessary action.

Signed-off-by: Yufeng Mo <moyufeng@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>