MEDIUM: task: extend the state field to 32 bits

It's been too short for quite a while now and is now full. It's still
time to extend it to 32-bits since we have room for this without
wasting any space, so we now gained 16 new bits for future flags.

The values were not reassigned just in case there would be a few
hidden u16 or short somewhere in which these flags are placed (as
it used to be the case with stream->pending_events).

The patch is tagged MEDIUM because this required to update the task's
process() prototype to use an int instead of a short, that's quite a
bunch of places.
diff --git a/src/extcheck.c b/src/extcheck.c
index 4634731..6eaeac1 100644
--- a/src/extcheck.c
+++ b/src/extcheck.c
@@ -475,7 +475,7 @@
  * Please do NOT place any return statement in this function and only leave
  * via the out_unlock label.
  */
-struct task *process_chk_proc(struct task *t, void *context, unsigned short state)
+struct task *process_chk_proc(struct task *t, void *context, unsigned int state)
 {
 	struct check *check = context;
 	struct server *s = check->server;