MEDIUM: add set-priority-class and set-priority-offset

This adds the set-priority-class and set-priority-offset actions to
http-request and tcp-request content. At this point they are not used
yet, which is the purpose of the next commit, but all the logic to
set and clear the values is there.
diff --git a/include/types/stream.h b/include/types/stream.h
index a3137bf..feeb56b 100644
--- a/include/types/stream.h
+++ b/include/types/stream.h
@@ -131,6 +131,8 @@
 	struct task *task;              /* the task associated with this stream */
 	unsigned short pending_events;	/* the pending events not yet processed by the stream.
 					 * This is a bit field of TASK_WOKEN_* */
+	int16_t priority_class;         /* priority class of the stream for the pending queue */
+	int32_t priority_offset;        /* priority offset of the stream for the pending queue */
 
 	struct list list;               /* position in global streams list */
 	struct list by_srv;             /* position in server stream list */