!8868 ipv6: prevent NULL dereference in ip6_output()

Merge Pull Request from: @ci-robot 
 
PR sync from: Liu Jian <liujian56@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/BRT7RJMBDD26HLUJ2KC7ILA3LIZ6PKR4/ 
 
https://gitee.com/src-openeuler/kernel/issues/I9UO9S 
 
Link:https://gitee.com/openeuler/kernel/pulls/8868

 

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