feat(esp_netif): Add support for esp_netif with custom TCP/IP stack

Added a new Kconfig option ESP_NETIF_PROVIDE_CUSTOM_IMPLEMENTATION which
uses only esp_netif headers, no implementation is provided and expected
to be supplied by application layer.

components/esp_netif/Kconfig

@@ -13,9 +13,18 @@ menu "ESP NETIF Adapter"
             the timer expires. The IP lost timer is stopped if the station get the IP again before
             the timer expires.
 
+    config ESP_NETIF_PROVIDE_CUSTOM_IMPLEMENTATION
+        bool "Use only ESP-NETIF headers"
+        default n
+        help
+            No implementation of ESP-NETIF functions is provided.
+            This option is used for adding a custom TCP/IP stack and defining related
+            esp_netif functionality
+
     choice ESP_NETIF_USE_TCPIP_STACK_LIB
         prompt "TCP/IP Stack Library"
         default ESP_NETIF_TCPIP_LWIP
+        depends on !ESP_NETIF_PROVIDE_CUSTOM_IMPLEMENTATION
         help
             Choose the TCP/IP Stack to work, for example, LwIP, uIP, etc.
         config ESP_NETIF_TCPIP_LWIP

components/esp_netif/loopback/esp_netif_loopback.c

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2015-2022 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2015-2024 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -465,4 +465,19 @@ esp_err_t esp_netif_remove_ip6_address(esp_netif_t *esp_netif, const esp_ip6_add
     return ESP_ERR_NOT_SUPPORTED;
 }
 
+int esp_netif_get_all_ip6(esp_netif_t *esp_netif, esp_ip6_addr_t if_ip6[])
+{
+    return 0;
+}
+
+esp_ip6_addr_type_t esp_netif_ip6_get_addr_type(esp_ip6_addr_t* ip6_addr)
+{
+    return ESP_IP6_ADDR_IS_UNKNOWN;
+}
+
+esp_err_t esp_netif_tcpip_exec(esp_netif_callback_fn fn, void*ctx)
+{
+    return fn(ctx);
+}
+
 #endif /* CONFIG_ESP_NETIF_LOOPBACK */