feat(linux): added esp_wifi mocking support

tools/mocks/esp_netif/include/esp_netif_mock.h

@@ -0,0 +1,15 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+/**
+ * Since esp_netif_obj is an opaque type (not defined, just declared), we define it here
+ * since its size is required by some of the mock functions.
+ */
+struct esp_netif_obj {
+    void *dummy;
+};