Bluetooth: Add public l2cap_conn_shutdown() API to request disconnection

Since we no-longer do special handling of SMP within l2cap_core.c we
don't have any code for calling l2cap_conn_del() when smp.c doesn't like
the data it gets. At the same time we cannot simply export
l2cap_conn_del() since it will try to lock the channels it calls into
whereas we already hold the lock in the smp.c l2cap_chan callbacks (i.e.
it'd lead to a deadlock).

This patch adds a new l2cap_conn_shutdown() API which is very similar to
l2cap_conn_del() except that it defers the call to l2cap_conn_del()
through a workqueue, thereby making it safe to use it from an L2CAP
channel callback.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

include/net/bluetooth/l2cap.h

@@ -625,6 +625,9 @@ struct l2cap_conn {
 
 	struct delayed_work	info_timer;
 
+	int			disconn_err;
+	struct work_struct	disconn_work;
+
 	struct sk_buff		*rx_skb;
 	__u32			rx_len;
 	__u8			tx_ident;
@@ -944,6 +947,7 @@ void l2cap_logical_cfm(struct l2cap_chan *chan, struct hci_chan *hchan,
 		       u8 status);
 void __l2cap_physical_cfm(struct l2cap_chan *chan, int result);
 
+void l2cap_conn_shutdown(struct l2cap_conn *conn, int err);
 void l2cap_conn_get(struct l2cap_conn *conn);
 void l2cap_conn_put(struct l2cap_conn *conn);