batman-adv: Avoid WARN_ON timing related checks

mainline inclusion
from mainline-v5.13-rc7
commit 9f460ae3
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9R4GZ
CVE: CVE-2021-47252

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9f460ae31c4435fd022c443a6029352217a16ac1



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The soft/batadv interface for a queued OGM can be changed during the time
the OGM was queued for transmission and when the OGM is actually
transmitted by the worker.

But WARN_ON must be used to denote kernel bugs and not to print simple
warnings. A warning can simply be printed using pr_warn.

Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Reported-by:  <syzbot+c0b807de416427ff3dd1@syzkaller.appspotmail.com>
Fixes: ef0a937f ("batman-adv: consider outgoing interface in OGM sending")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: He Yujie <coka.heyujie@huawei.com>