Bluetooth: Fix rejected connection not disconnecting ACL link

When using DEFER_SETUP on a RFCOMM socket, a SABM frame triggers
authorization which when rejected send a DM response. This is fine
according to the RFCOMM spec:

    the responding implementation may replace the "proper" response
    on the Multiplexer Control channel with a DM frame, sent on the
    referenced DLCI to indicate that the DLCI is not open, and that
    the responder would not grant a request to open it later either.

But some stacks doesn't seems to cope with this leaving DLCI 0 open after
receiving DM frame.

To fix it properly a timer was introduced to rfcomm_session which is used
to set a timeout when the last active DLC of a session is unlinked, this
will give the remote stack some time to reply with a proper DISC frame on
DLCI 0 avoiding both sides sending DISC to each other on stacks that
follow the specification and taking care of those who don't by taking
down DLCI 0.

Signed-off-by: Luiz Augusto von Dentz <luiz.dentz@openbossa.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

include/net/bluetooth/rfcomm.h

@@ -29,6 +29,7 @@
 #define RFCOMM_CONN_TIMEOUT (HZ * 30)
 #define RFCOMM_DISC_TIMEOUT (HZ * 20)
 #define RFCOMM_AUTH_TIMEOUT (HZ * 25)
+#define RFCOMM_IDLE_TIMEOUT (HZ * 2)
 
 #define RFCOMM_DEFAULT_MTU	127
 #define RFCOMM_DEFAULT_CREDITS	7
@@ -154,6 +155,7 @@ struct rfcomm_msc {
 struct rfcomm_session {
 	struct list_head list;
 	struct socket   *sock;
+	struct timer_list timer;
 	unsigned long    state;
 	unsigned long    flags;
 	atomic_t         refcnt;