Cellular: Fix setting of PDP context ID (cid)

UNITTESTS/stubs/AT_CellularContext_stub.cpp

@@ -279,6 +279,10 @@ void AT_CellularContext::set_disconnect()
 {
 }
 
+void AT_CellularContext::set_cid(int cid)
+{
+}
+
 void AT_CellularContext::do_connect_with_retry()
 {
 

UNITTESTS/stubs/AT_CellularStack_stub.cpp

@@ -94,3 +94,6 @@ void AT_CellularStack::socket_attach(nsapi_socket_t handle, void (*callback)(voi
 {
 }
 
+void AT_CellularStack::set_cid(int cid)
+{
+}

UNITTESTS/target_h/myCellularContext.h

@@ -216,6 +216,10 @@ public:
     {
     };
 
+    void set_cid(int cid)
+    {
+    };
+
     void do_connect_with_retry()
     {
     };

features/cellular/framework/AT/AT_CellularContext.cpp

@@ -299,7 +299,7 @@ void AT_CellularContext::delete_current_context()
     _at.at_cmd_discard("+CGDCONT", "=", "%d", _cid);
 
     if (_at.get_last_error() == NSAPI_ERROR_OK) {
-        _cid = -1;
+        set_cid(-1);
         _new_context_set = false;
     }
 
@@ -347,7 +347,7 @@ bool AT_CellularContext::get_context()
 {
     _at.cmd_start_stop("+CGDCONT", "?");
     _at.resp_start("+CGDCONT:");
-    _cid = -1;
+    set_cid(-1);
     int cid_max = 0; // needed when creating new context
     char apn[MAX_ACCESSPOINT_NAME_LENGTH];
     int apn_len = 0;
@@ -373,7 +373,7 @@ bool AT_CellularContext::get_context()
                 if (get_property(pdp_type_t_to_cellular_property(pdp_type)) ||
                         ((pdp_type == IPV4V6_PDP_TYPE && (get_property(PROPERTY_IPV4_PDP_TYPE) && get_property(PROPERTY_IPV6_PDP_TYPE))) && !_nonip_req)) {
                     _pdp_type = pdp_type;
-                    _cid = cid;
+                    set_cid(cid);
                 }
             }
         }
@@ -423,7 +423,7 @@ bool AT_CellularContext::set_new_context(int cid)
 
     if (success) {
         _pdp_type = pdp_type;
-        _cid = cid;
+        set_cid(cid);
         _new_context_set = true;
         tr_info("New PDP context %d, type %d", _cid, pdp_type);
     }
@@ -661,7 +661,7 @@ void AT_CellularContext::do_disconnect()
         if (_new_context_set) {
             delete_current_context();
         }
-        _cid = -1;
+        set_cid(-1);
         _cb_data.error = NSAPI_ERROR_NO_CONNECTION;
     }
 
@@ -697,7 +697,7 @@ void AT_CellularContext::do_disconnect()
     if (_new_context_set) {
         delete_current_context();
     }
-    _cid = -1;
+    set_cid(-1);
     _cb_data.error = _at.unlock_return_error();
 }
 
@@ -994,6 +994,7 @@ void AT_CellularContext::cellular_callback(nsapi_event_t ev, intptr_t ptr)
             } else if (ev == NSAPI_EVENT_CONNECTION_STATUS_CHANGE && ptr == NSAPI_STATUS_DISCONNECTED) {
                 tr_info("cellular_callback: PPP mode and NSAPI_STATUS_DISCONNECTED");
                 _cb_data.error = NSAPI_ERROR_NO_CONNECTION;
+                set_cid(-1);
                 _is_connected = false;
                 ppp_disconnected();
             }
@@ -1001,6 +1002,7 @@ void AT_CellularContext::cellular_callback(nsapi_event_t ev, intptr_t ptr)
 #else
         if (ev == NSAPI_EVENT_CONNECTION_STATUS_CHANGE && ptr == NSAPI_STATUS_DISCONNECTED) {
             tr_info("cb: CellularContext disconnected");
+            set_cid(-1);
             _is_connected = false;
         }
 #endif // NSAPI_PPP_AVAILABLE
@@ -1065,3 +1067,11 @@ void AT_CellularContext::set_disconnect()
     _is_connected = false;
     _device->cellular_callback(NSAPI_EVENT_CONNECTION_STATUS_CHANGE, NSAPI_STATUS_DISCONNECTED, this);
 }
+
+void AT_CellularContext::set_cid(int cid)
+{
+    _cid = cid;
+    if (_stack) {
+        static_cast<AT_CellularStack *>(_stack)->set_cid(_cid);
+    }
+}

features/cellular/framework/AT/AT_CellularContext.h

@@ -119,6 +119,7 @@ private:
     void ciot_opt_cb(mbed::CellularNetwork::CIoT_Supported_Opt ciot_opt);
     virtual void do_connect_with_retry();
     void do_disconnect();
+    void set_cid(int cid);
 private:
     bool _is_connected;
     ContextOperation  _current_op;

features/cellular/framework/AT/AT_CellularStack.cpp

@@ -98,6 +98,11 @@ const char *AT_CellularStack::get_ip_address()
     return (ipv4 || ipv6) ? _ip : NULL;
 }
 
+void AT_CellularStack::set_cid(int cid)
+{
+    _cid = cid;
+}
+
 nsapi_error_t AT_CellularStack::socket_stack_init()
 {
     return NSAPI_ERROR_OK;

features/cellular/framework/AT/AT_CellularStack.h

@@ -44,6 +44,14 @@ public:
 public: // NetworkStack
 
     virtual const char *get_ip_address();
+
+    /**
+     * Set PDP context ID for this stack
+     *
+     *  @param cid value from AT+CGDCONT, where -1 is undefined
+     */
+    void set_cid(int cid);
+
 protected: // NetworkStack
 
     /**