Bluetooth: Stop BCSP/H5 timer before cleaning up

When stopping BCSP/H5, stop the retransmission timer before proceeding
to clean up packet queues.  The previous code had a race condition where
the timer could trigger after the packet lists and protocol structure
had been removed which led to dereferencing NULL or use-after-free bugs.

Signed-off-by: Michael Knudsen <m.knudsen@samsung.com>
Reported-by: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>