Change NGHTTP2_INITIAL_MAX_CONCURRENT_STREAMS

The previous value 100 is non-standard, and if it is not sent with
SETTINGS, session will be closed with protocol error.

lib/includes/nghttp2/nghttp2.h

@@ -359,7 +359,7 @@ typedef enum {
  * @macro
  * Default maximum concurrent streams.
  */
-#define NGHTTP2_INITIAL_MAX_CONCURRENT_STREAMS 100
+#define NGHTTP2_INITIAL_MAX_CONCURRENT_STREAMS ((1U << 31) - 1)
 
 /**
  * @enum