net: hns3: disable loopback setting in hclge_mac_init

If the selftest and reset are performed at the same time, the loopback
setting may be still in the enable state after the reset. As a result,
packets cannot be sent out.

This patch fixes this issue by disabling loopback in hclge_mac_init.

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>