Bluetooth: L2CAP: fix "bad unlock balance" in l2cap_disconnect_rsp

stable inclusion
from stable-v5.10.181
commit 55410a9144c76ecda126e6cdec556dfcd8f343b2
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8GJZJ

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=55410a9144c76ecda126e6cdec556dfcd8f343b2



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[ Upstream commit 25e97f7b ]

conn->chan_lock isn't acquired before l2cap_get_chan_by_scid,
if l2cap_get_chan_by_scid returns NULL, then 'bad unlock balance'
is triggered.

Reported-by:  <syzbot+9519d6b5b79cf7787cf3@syzkaller.appspotmail.com>
Link: https://lore.kernel.org/all/000000000000894f5f05f95e9f4d@google.com/


Signed-off-by: Min Li <lm0963hack@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>
(cherry picked from commit 7c03ca3b)