fix(modem): Fix netif to set PPP config in C++ way

If the config struct contains more items (or more items will be added in
future) this init will not compile cleanly

components/esp_modem/src/esp_modem_netif.cpp

@@ -49,9 +49,9 @@ esp_err_t Netif::esp_modem_post_attach(esp_netif_t *esp_netif, void *args)
     ESP_ERROR_CHECK(esp_netif_set_driver_config(esp_netif, &driver_ifconfig));
     // check if PPP error events are enabled, if not, do enable the error occurred/state changed
     // to notify the modem layer when switching modes
-    esp_netif_ppp_config_t ppp_config = { .ppp_phase_event_enabled = true,    // assuming phase enabled, as earlier IDFs
-                                          .ppp_error_event_enabled = false
-                                        }; // don't provide cfg getters so we enable both events
+    esp_netif_ppp_config_t ppp_config = { };
+    ppp_config.ppp_phase_event_enabled = true;    // assuming phase enabled, as earlier IDFs
+    ppp_config.ppp_error_event_enabled = false;   // don't provide cfg getters so we enable both events
 #if ESP_IDF_VERSION >= ESP_IDF_VERSION_VAL(4, 4, 0)
     esp_netif_ppp_get_params(esp_netif, &ppp_config);
 #endif // ESP-IDF >= v4.4