diag: dci: Mutex protect the list while traversal and node deletion

On receiving the response from peripherals for the sent command
DCI traverses and deletes from the list. The list is not lock
protected while traversal or deletion. This patch resolves the
same.

Change-Id: Ie93f3e035b35c4d39f1e19f9c42a48f4147fe145
CRs-Fixed: 715663
Signed-off-by: Katish Paran <kparan@codeaurora.org>