[Bluetooth]: Don't update disconnect timer for incoming connections

In the case of device pairing the only safe method is to establish
a low-level ACL link. In this case, the remote side should not use
the disconnect timer to give the other side the chance to enter the
PIN code. If the disconnect timer is used, the connection will be
dropped to soon, because it is impossible to identify an actual user
of this link.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: David S. Miller <davem@davemloft.net>