net: hns3: support ndo_select_queue()

To support tx packets to select queue according to its dscp field after
setting dscp and tc map relationship, this patch implements
ndo_select_queue() to set skb->priority according to the user's setting
dscp and priority map relationship.

Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>