MEDIUM: threads/tasks: Add lock around notifications

This patch add lock around some notification calls
diff --git a/include/types/task.h b/include/types/task.h
index da7c929..799e6c5 100644
--- a/include/types/task.h
+++ b/include/types/task.h
@@ -56,6 +56,9 @@
 	struct list wake_me; /* Part of list of signals to be targeted if an
 	                        event occurs. */
 	struct task *task; /* The task to be wake if an event occurs. */
+#ifdef USE_THREAD
+	HA_SPINLOCK_T lock;
+#endif
 };
 
 /* The base for all tasks */