Fix for compiling with lwIP (3)

lwIP on Windows does not have a WSAIoctl() function. 
But it do have a SO_SNDBUF option to lwip_setsockopt(). But it currently does nothing.

lib/transfer.c

@@ -879,7 +879,7 @@ static CURLcode done_sending(struct connectdata *conn,
   return CURLE_OK;
 }
 
-#ifdef WIN32
+#if defined(WIN32) && !defined(USE_LWIPSOCK)
 #ifndef SIO_IDEAL_SEND_BACKLOG_QUERY
 #define SIO_IDEAL_SEND_BACKLOG_QUERY 0x4004747B
 #endif