add RTT 4.1.0 support

src/agile_telnet.c

@@ -40,11 +40,13 @@
 #include <agile_telnet.h>
 #include <agile_console.h>
 
-#include <dfs_posix.h>
 #if RT_VER_NUM < 0x40100
+#include <dfs_posix.h>
 #include <dfs_poll.h>
 #else
+#include <dfs_file.h>
 #include <poll.h>
+#include <unistd.h>
 #endif
 #include <sys/time.h>
 #include <sys/socket.h>