bluetooth: delete retransmit timer after ibs workqueue destructs

Wake retransmit timer is modified in two places, namely in timer handler
and in work to awake remote controller. Retransmit timer is deleted during
IBS protocol close.
In cases where IBS close is racing with awake work, timer handler will
execute after freeing of protocol resulting in crash. Hence, delete the
workqueue first so that no more awake work can be enqueued and then delete
the retransmit timer.

CRs-Fixed: 965303
Change-Id: I3f1ee4c21d6136e12267e9d8c35db02f1f3ae08c
Signed-off-by: Rupesh Tatiya <rtatiya@codeaurora.org>