csdk: prevent release build compiler warning from log tags

csdk: prevent release build compiler warning from log tags

Changed `static char const TAG[]` used for logging to `#define TAG`
to prevent -Wunused-const-variable= warning when building code
in release mode.

Change-Id: Idaebfb26863a3a812573c8c40065ad9ff6ea356d
Signed-off-by: George Nash <george.nash@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/17753
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>