GEMALTO CINTERION: add 1ms sleep in socket sendto

Author: pennam

connectivity/drivers/cellular/GEMALTO/CINTERION/GEMALTO_CINTERION_CellularStack.cpp

@@ -19,6 +19,7 @@
 #include "GEMALTO_CINTERION_CellularStack.h"
 #include "GEMALTO_CINTERION.h"
 #include "CellularLog.h"
+#include "platform/mbed_thread.h"
 #include "rtos.h"
 
 using namespace std::chrono_literals;
@@ -538,6 +539,8 @@ nsapi_size_or_error_t GEMALTO_CINTERION_CellularStack::socket_sendto_impl(Cellul
         socket->tx_ready = false;
     }
 
+    thread_sleep_for(1);  // wait for modem to process the data;
+
     return (_at.get_last_error() == NSAPI_ERROR_OK) ? accept_len : NSAPI_ERROR_DEVICE_ERROR;
 }