diag: Add support for diag dci restart

The diag implementation of dci does not properly
handle the closing/re-opening of the dci channel.
Add support for closing/re-opening of the dci channel
including appropriate handling of client dci requests while
the channel is closed and resumption upon re-opening of
the channel.

Change-Id: Ied29fe99be5fee34cfe27cc5bdeacd4365fa136b
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>