diag: Add mutex protection while closing SMD

On receiving feature mask add mutex protection while closing
SMD and start reading from socket channel.

CRs-Fixed: 980999
Change-Id: I01e5e8c9e0b03fa8b09f0ffd6857fe7e60a48091
Signed-off-by: Sreelakshmi Gownipalli <sgownipa@codeaurora.org>
Signed-off-by: Mohit Aggarwal <maggarwa@codeaurora.org>
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>