Adjust the minimum value of h2_initial_window_size

We have a strict min at the protocol default here. This is because we
don't have the 'use settings only after peer ack' in place yet. If the
value is lower than the protocol default, the very first stream could get
a flow control error.

include/tbl/params.h

@@ -1195,15 +1195,19 @@ PARAM_SIMPLE(
 	"at the same time for a single HTTP2 connection."
 )
 
+/* We have a strict min at the protocol default here. This is because we
+ * don't have the 'use settings only after peer ack' in place yet. If the
+ * value is lower than the protocol default, the very first stream could
+ * get a flow control error. */
 PARAM_SIMPLE(
 	/* name */	h2_initial_window_size,
 	/* type */	bytes_u,
-	/* min */	"0",
+	/* min */	"65535b",
 	/* max */	"2147483647b",
 	/* def */	"65535b",
 	/* units */	"bytes",
 	/* descr */
-	"HTTP2 initial flow control window size."
+	"HTTP2 initial flow control window size.",
 )
 
 PARAM_SIMPLE(