net: hns3: remove unnecessary frag list checking in hns3_nic_net_xmit()

The skb_has_frag_list() in hns3_nic_net_xmit() is redundant, since
skb_walk_frags() includes this checking implicitly.

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