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

jira VULN-154997
cve CVE-2023-53297
commit-author Min Li <[email protected]>
commit 25e97f7

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: [email protected]
Link: https://lore.kernel.org/all/[email protected]/
	Signed-off-by: Min Li <[email protected]>
	Signed-off-by: Luiz Augusto von Dentz <[email protected]>
(cherry picked from commit 25e97f7)
	Signed-off-by: Roxana Nicolescu <[email protected]>

Author: roxanan1996

net/bluetooth/l2cap_core.c

@@ -4675,7 +4675,6 @@ static inline int l2cap_disconnect_rsp(struct l2cap_conn *conn,
 
 	chan = l2cap_get_chan_by_scid(conn, scid);
 	if (!chan) {
-		mutex_unlock(&conn->chan_lock);
 		return 0;
 	}