broadband-modem-mbim: add AT based fallback to load model name

Modify the load_model function to use the AT command to get the
model name and display the module name in the model instead of
[vid:pid].
Test on L860 Linux Device, use `mmcli -L`, it can show: "/org/free
desktop/ModemManager1/Modem/0 [Intel] L860-GL-16 LTE Module"

src/mm-broadband-modem-mbim.c

@@ -65,6 +65,7 @@ static void shared_qmi_init                       (MMSharedQmi
 static MMIfaceModemLocation *iface_modem_location_parent;
 #endif
 static MMIfaceModemSignal *iface_modem_signal_parent;
+static MMIfaceModem       *iface_modem_parent;
 
 G_DEFINE_TYPE_EXTENDED (MMBroadbandModemMbim, mm_broadband_modem_mbim, MM_TYPE_BROADBAND_MODEM, 0,
                         G_IMPLEMENT_INTERFACE (MM_TYPE_IFACE_MODEM, iface_modem_init)
@@ -816,6 +817,25 @@ qmi_load_model_ready (MMIfaceModem *self,
 
 #endif
 
+static void
+at_load_model_ready (MMIfaceModem *self,
+                     GAsyncResult *res,
+                     GTask        *task)
+{
+    gchar  *model = NULL;
+    GError *error = NULL;
+
+    model = iface_modem_parent->load_model_finish (self, res, &error);
+    if (!model) {
+        mm_obj_dbg (self, "couldn't load model using AT: %s", error->message);
+        model = modem_load_model_default (self);
+        g_clear_error (&error);
+    }
+
+    g_task_return_pointer (task, model, g_free);
+    g_object_unref (task);
+}
+
 static void
 modem_load_model (MMIfaceModem *self,
                   GAsyncReadyCallback callback,
@@ -831,6 +851,11 @@ modem_load_model (MMIfaceModem *self,
     if (port) {
         model = g_strdup (mm_kernel_device_get_physdev_product (
             mm_port_peek_kernel_device (MM_PORT (port))));
+        if (model) {
+            g_task_return_pointer (task, model, g_free);
+            g_object_unref (task);
+            return;
+        }
     }
 
 #if defined WITH_QMI && QMI_MBIM_QMUX_SUPPORTED
@@ -840,11 +865,7 @@ modem_load_model (MMIfaceModem *self,
     }
 #endif
 
-    if (!model)
+    iface_modem_parent->load_model (self, (GAsyncReadyCallback)at_load_model_ready, task);
-        model = modem_load_model_default (self);
-
-    g_task_return_pointer (task, model, g_free);
-    g_object_unref (task);
 }
 
 /*****************************************************************************/
@@ -9238,6 +9259,7 @@ finalize (GObject *object)
 static void
 iface_modem_init (MMIfaceModem *iface)
 {
+    iface_modem_parent = g_type_interface_peek_parent (iface);
     /* Initialization steps */
     iface->load_supported_capabilities = modem_load_supported_capabilities;
     iface->load_supported_capabilities_finish = modem_load_supported_capabilities_finish;