modify AT_CellularDevice_stub to pass test with the new feature

Author: Tobi15

connectivity/cellular/tests/UNITTESTS/doubles/AT_CellularDevice_stub.cpp

@@ -33,9 +33,9 @@ bool AT_CellularDevice_stub::pin_needed = false;
 bool AT_CellularDevice_stub::supported_bool = false;
 int AT_CellularDevice_stub::max_sock_value = 1;
 
-AT_CellularDevice::AT_CellularDevice(FileHandle *fh) :
+AT_CellularDevice::AT_CellularDevice(FileHandle *fh, char* delim) :
     CellularDevice(),
-    _at(fh, _queue, get_property(AT_CellularDevice::PROPERTY_AT_SEND_DELAY), "\r"),
+    _at(fh, _queue, get_property(AT_CellularDevice::PROPERTY_AT_SEND_DELAY), delim),
 #if MBED_CONF_CELLULAR_USE_SMS
     _sms(0),
 #endif // MBED_CONF_CELLULAR_USE_SMS