Windows: Increase connection limit to 8192 where supported.

Closes #2732. Thanks to zhousongsong.

ChangeLog.txt

@@ -7,6 +7,8 @@ Broker:
   assertions removed. Closes #2708.
 - Fix default settings incorrectly allowing TLS v1.1. Closes #2722.
 - Use line buffered mode for stdout. Closes #2354. Closes #2749.
+- Fix connections being limited to 2048 on Windows. The limit is now 8192,
+  where supported. Closes #2732.
 
 Client library:
 - Use CLOCK_BOOTTIME when available, to keep track of time. This solves the

src/mosquitto.c

@@ -484,7 +484,12 @@ int main(int argc, char *argv[])
 #endif
 
 #ifdef WIN32
-	_setmaxstdio(2048);
+	if(_setmaxstdio(8192) != 8192){
+		/* Old limit was 2048 */
+		if(_setmaxstdio(2048) != 2048){
+			log__printf(NULL, MOSQ_LOG_WARNING, "Warning: Unable to increase maximum allowed connections. This session may be limited to 512 connections.");
+		}
+	}
 #endif
 
 	memset(&db, 0, sizeof(struct mosquitto_db));