Bluetooth: timer check sk is not owned before freeing

In timer context we might delete l2cap channel used by krfcommd.
The check makes sure that sk is not owned. If sk is owned we
restart timer for HZ/5.

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>