Bluetooth: ATT: Add timeout handling

Accourding to the spec request should have a timeout of 30 seconds:

BLUETOOTH SPECIFICATION Version 4.2 [Vol 3, Part F] page 480:

  'A transaction not completed within 30 seconds shall time out. Such a
   transaction shall be considered to have failed and the local higher
   layers shall be informed of this failure. No more attribute protocol
   requests, commands, indications or notifications shall be sent to the
   target device on this ATT Bearer.'

Change-Id: I5e5b9fb008d3019831c5f6cc3bd4c2b85dd6b90a
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>