MINOR: connections/mux: Add the wait reason(s) to wait_list.

Add a new element to the wait_list, that let us know which event(s) we are
waiting on.
diff --git a/include/proto/connection.h b/include/proto/connection.h
index e4621cc..35b9dfe 100644
--- a/include/proto/connection.h
+++ b/include/proto/connection.h
@@ -601,6 +601,7 @@
 	LIST_INIT(&cs->wait_list.list);
 	LIST_INIT(&cs->send_wait_list);
 	cs->conn = conn;
+	cs->wait_list.wait_reason = 0;
 }
 
 /* Initializes all required fields for a new connection. Note that it does the