Merge pull request #14 from armink-rtt-pkgs/master

【修正】CMUX 长帧收发出错的问题。完善 AT+CMUX 参数，增加长帧的支持

src/gsm/cmux_gsm.c

@@ -24,7 +24,9 @@
 #endif
 #include <rtdbg.h>
 
-#define CMUX_CMD "AT+CMUX=0"
+#ifndef CMUX_CMD
+#define CMUX_CMD "AT+CMUX=0,0,5,2048,20,3,30,10,2"
+#endif
 
 struct cmux *gsm = RT_NULL;