net/hns3: fix Tx checksum outer header prepare

net/hns3: fix Tx checksum outer header prepare

Currently, there are two mistakes in Tx checksum outer header prepare.
1) Check whether the packet outer header is IPV4 based on PKT_TX_IPV4
   which is incorrect.
2) For HIP08, the outer UDP cksum could not be offloaded. And driver
   should ensure the outer udp cksum filed set to 0. In current code,
   PKT_TX_UDP_CKSUM is used to determine whether the outer layer of
   the packet is a UDP header. Actually, for tunnel TSO, the flag will
   never be set.

For the first mistake, it is fixed by replacing PKT_TX_IPV4 with
PKT_TX_OUTER_IPV4. And the protocol number in L3 header is used to check
whether the outer L4 header is UDP.

Fixes: bba636698316 ("net/hns3: support Rx/Tx and related operations")
Fixes: 6dca716c9e1d ("net/hns3: support TSO")
Cc: stable@dpdk.org
Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
Signed-off-by: Lijun Ou <oulijun@huawei.com>