change default value of TCP_SND_BUF to 2048.

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@352 bbd45198-f89e-11dd-88c7-29a3b14d5316

net/lwip/src/lwipopts.h

@@ -182,7 +182,7 @@
 #ifdef RT_LWIP_TCP_SND_BUF
 #define TCP_SND_BUF                 RT_LWIP_TCP_SND_BUF
 #else
-#define TCP_SND_BUF                 1024
+#define TCP_SND_BUF                 2048
 #endif
 
 /* TCP sender buffer space (pbufs). This must be at least = 2 *