Watchdog race condition when sending message out of synchronized

A race condition leading to false positive detections might occur
when the monitoring thread executes very fast and terminates before
the sending thread entered the synchronized section.

Change-Id: I6fe686f8f12393e11fa18326508af5b73738f9d7
Author: Jean-Christophe PINCE <jean-christophe.pince@intel.com>
Signed-off-by: Jean-Christophe PINCE <jean-christophe.pince@intel.com>
Signed-off-by: Shuo Gao <shuo.gao@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>
Signed-off-by: Jack Ren <jack.ren@intel.com>
Author-tracking-BZ: 81644