poll: Add a max_delay parameter to PollController::expireTimedout

Currently the maximum additional delay is hard coded to 13. This
value depends on the source of the frame number value.

This commit adds the max_delay parameter to make it caller dependant.

Sponsored-by: On-Waves ehf
diff --git a/src/poll_controller.h b/src/poll_controller.h
index dac3e6d..b9ae80e 100644
--- a/src/poll_controller.h
+++ b/src/poll_controller.h
@@ -34,7 +34,8 @@
 public:
 	PollController(BTS& bts);
 
-	void expireTimedout(int frame_number);
+	/* check for poll timeout */
+	void expireTimedout(int frame_number, unsigned max_delay);
 
 private:
 	BTS& m_bts;