MINOR: tasks: Add a flag that tells if we're in the global runqueue.

How that we have bits available in task->state, add a flag that tells if we're
in the global runqueue or not.
diff --git a/include/proto/task.h b/include/proto/task.h
index 8aceee5..3969dc3 100644
--- a/include/proto/task.h
+++ b/include/proto/task.h
@@ -181,6 +181,8 @@
 {
 	HA_ATOMIC_SUB(&tasks_run_queue, 1);
 	eb32sc_delete(&t->rq);
+	if (t->state & TASK_GLOBAL)
+		HA_ATOMIC_AND(&t->state, ~TASK_GLOBAL);
 	if (likely(t->nice))
 		HA_ATOMIC_SUB(&niced_tasks, 1);
 	return t;