param: New h2_window_timeout parameter

This parameter needs to be somewhat high because web browsers may for
example only credit streams for image resources just enough to parse
metadata like width and height of a picture in order to perform layout
computations and fetch resources more sensitive to latency before the
effective image payloads.

include/tbl/params.h

@@ -1205,6 +1205,20 @@ PARAM_SIMPLE(
 	/* flags */	WIZARD
 )
 
+PARAM_SIMPLE(
+	/* name */	h2_window_timeout,
+	/* type */	timeout,
+	/* min */	"0",
+	/* max */	NULL,
+	/* def */	"5",
+	/* units */	"seconds",
+	/* descr */
+	"HTTP2 time limit without window credits. How long a stream may "
+	"wait for the client to credit the window and allow for more DATA "
+	"frames to be sent.",
+	/* flags */	WIZARD
+)
+
 PARAM_SIMPLE(
 	/* name */	h2_header_table_size,
 	/* type */	bytes_u,