GEMALTO CINTERION: fix enable cmux command

Author: pennam

connectivity/cellular/source/framework/AT/AT_CellularDevice.cpp

@@ -50,6 +50,7 @@ AT_CellularDevice::AT_CellularDevice(FileHandle *fh, char *delim):
     _context_list(0),
     _default_timeout(DEFAULT_AT_TIMEOUT),
     _modem_debug_on(false),
+    _cmux_status(false),
     _property_array(NULL)
 {
     MBED_ASSERT(fh);
@@ -243,10 +244,10 @@ nsapi_error_t AT_CellularDevice::get_sim_state(SimState &state)
 
 nsapi_error_t AT_CellularDevice::enable_cmux()
 {
-setup_at_handler();
-
+    setup_at_handler();
     _at.lock();
     for (int retry = 1; retry <= 3; retry++) {
+        is_ready();
         _at.clear_error();
         _at.flush();
         _at.at_cmd_discard("E0", "");
@@ -259,10 +260,9 @@ setup_at_handler();
         tr_debug("Wait 100ms to init modem");
         rtos::ThisThread::sleep_for(100ms); // let modem have time to get ready
     }
- return _at.unlock_return_error();
+    return _at.unlock_return_error();
 }
 
-
 bool AT_CellularDevice::is_cmux_enabled()
 {
     return _cmux_status;
@@ -272,6 +272,7 @@ void AT_CellularDevice::set_cmux_status_flag(bool cmux_status)
 {
     _cmux_status = cmux_status;
 }
+
 nsapi_error_t AT_CellularDevice::set_pin(const char *sim_pin)
 {
     // if SIM is already in ready state then settings the PIN