!4601 v2 xen-netback: don't produce zero-size SKB frags

Merge Pull Request from: @ci-robot 
 
PR sync from: Ziyang Xuan <william.xuanziyang@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/TRAHE6677V5YCUKY4HGR3YXMFUNY7HYX/ 
 
https://gitee.com/src-openeuler/kernel/issues/I8YCSC 
 
Link:https://gitee.com/openeuler/kernel/pulls/4601

 

Reviewed-by: Liu YongQiang <liuyongqiang13@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>