net: hns3: Refactor the skb receiving and transmitting function

This patch refactors the skb receiving and transmitting functions
and export them in order to support the ethtool's mac loopback
selftest.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>