Cellular: AT_CellularContext disconnect in non-blocking mode

Disconnect was supporting only blocking mode.

UNITTESTS/features/cellular/framework/AT/at_cellularcontext/at_cellularcontexttest.cpp

@@ -603,15 +603,22 @@ TEST_F(TestAT_CellularContext, connect_disconnect_async)
     ASSERT_EQ(network_cb_count, 5);
     ASSERT_EQ(ctx1.connect(), NSAPI_ERROR_IS_CONNECTED);
     EXPECT_TRUE(ctx1.is_connected() == true);
+    ASSERT_EQ(ctx1.disconnect(), NSAPI_ERROR_NO_MEMORY);
+    EXPECT_TRUE(ctx1.is_connected() == true);
+
+    struct equeue_event ptr;
+    equeue_stub.void_ptr = &ptr;
+    equeue_stub.call_cb_immediately = true;
     ASSERT_EQ(ctx1.disconnect(), NSAPI_ERROR_OK);
     EXPECT_TRUE(ctx1.is_connected() == false);
 
     // sdet CellularDevice_stub::connect_counter = 0 so device is already attached and will return NSAPI_ERROR_ALREADY to context when calling connect
+    equeue_stub.void_ptr = &ptr;
+    equeue_stub.call_cb_immediately = false;
     CellularDevice_stub::connect_counter = 0;
     // queue can't allocate so return NSAPI_ERROR_NO_MEMORY
     ASSERT_EQ(ctx1.connect(), NSAPI_ERROR_NO_MEMORY);
 
-    struct equeue_event ptr;
     equeue_stub.void_ptr = &ptr;
     equeue_stub.call_cb_immediately = true;
     ASSERT_EQ(ctx1.connect(), NSAPI_ERROR_OK);

features/cellular/framework/AT/AT_CellularContext.cpp

@@ -59,6 +59,7 @@ AT_CellularContext::~AT_CellularContext()
 {
     tr_info("Delete CellularContext with apn: [%s] (%p)", _apn ? _apn : "", this);
 
+    _is_blocking = true;
     (void)disconnect();
 
     if (_nw) {
@@ -659,15 +660,14 @@ void AT_CellularContext::ppp_disconnected()
 
 #endif //#if NSAPI_PPP_AVAILABLE
 
-nsapi_error_t AT_CellularContext::disconnect()
+void AT_CellularContext::do_disconnect()
 {
-    tr_info("CellularContext disconnect()");
     if (!_nw || !_is_connected) {
         if (_new_context_set) {
             delete_current_context();
         }
         _cid = -1;
-        return NSAPI_ERROR_NO_CONNECTION;
+        _cb_data.error = NSAPI_ERROR_NO_CONNECTION;
     }
 
     // set false here so callbacks know that we are not connected and so should not send DISCONNECTED
@@ -703,8 +703,22 @@ nsapi_error_t AT_CellularContext::disconnect()
         delete_current_context();
     }
     _cid = -1;
+    _cb_data.error = _at.unlock_return_error();
+}
 
-    return _at.unlock_return_error();
+nsapi_error_t AT_CellularContext::disconnect()
+{
+    tr_info("CellularContext disconnect()");
+    if (_is_blocking) {
+        do_disconnect();
+        return _cb_data.error;
+    } else {
+        int event_id = _device->get_queue()->call_in(0, this, &AT_CellularContext::do_disconnect);
+        if (event_id == 0) {
+            return NSAPI_ERROR_NO_MEMORY;
+        }
+        return NSAPI_ERROR_OK;
+    }
 }
 
 void AT_CellularContext::deactivate_ip_context()

features/cellular/framework/AT/AT_CellularContext.h

@@ -118,6 +118,7 @@ private:
     nsapi_error_t check_operation(nsapi_error_t err, ContextOperation op);
     void ciot_opt_cb(mbed::CellularNetwork::CIoT_Supported_Opt ciot_opt);
     virtual void do_connect_with_retry();
+    void do_disconnect();
 private:
     bool _is_connected;
     ContextOperation  _current_op;