net: hns3: fix for vxlan gpe tx checksum bug

When skb->ip_summed is CHECKSUM_PARTIAL, for non-tunnel udp packet,
which has a dest port as the IANA assigned, the hardware is expected
to do the checksum offload, but the hardware whose version is below
V3 will not do the checksum offload when udp dest port is 4790.

So fixes it by doing the checksum in software for this case.

Fixes: 76ad4f0e

 ("net: hns3: Add support of HNS3 Ethernet Driver for hip08 SoC")
Signed-off-by: Hao Chen <chenhao288@hisilicon.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>