Bluetooth: L2CAP: Add timeout handling

This adds initial timeout handling as described in the spec:

BLUETOOTH SPECIFICATION Version 4.2 [Vol 3, Part A] page 126:

  'The value of this timer is implementation-dependent but the minimum
   initial value is 1 second and the maximum initial value is 60
   seconds. One RTX timer shall exist for each outstanding signaling
   request, including each Echo Request. The timer disappears on the
   final expiration, when the response is received, or the physical
   link is lost.'

Note: As for the actual interval used they are based on the values used
in Linux but in case of disconnect the minimum of 1 seconds was used
to follow the text above.

Change-Id: Ib98899c3ff07334955aee9c8fb53b1b89ba7bf31
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>