esp_netif: Introduction of esp-netif component as a replacement of tcpip_adpter

- provides object oriented access to network intefaces
- not limited to default netifs
- more generic abstraction to network input output functions
- event handler registration removed from component responsibility
- backward compatibility layer for legacy tcpip_apapter APIs

Closes IDF-39

components/esp_netif/include/esp_netif_net_stack.h

@@ -0,0 +1,41 @@
+// Copyright 2015-2019 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef _ESP_NETIF_NET_STACK_H_
+#define _ESP_NETIF_NET_STACK_H_
+
+//
+// Network stack API: This ESP-NETIF API are supposed to be called only from internals of TCP/IP stack
+//
+
+/**
+ * @brief Returns esp-netif handle
+ *
+ * @param[in] dev opaque ptr to network interface of specific TCP/IP stack
+ *
+ * @return    handle to related esp-netif instance
+ */
+esp_netif_t* esp_netif_get_handle_from_netif_impl(void *dev);
+
+
+/**
+ * @brief Returns network stack specific implementation handle
+ *
+ * @param[in]  esp_netif Handle to esp-netif instance
+ *
+ * @return    handle to related network stack netif handle
+ */
+void* esp_netif_get_netif_impl(esp_netif_t *esp_netif);
+
+#endif //_ESP_NETIF_NET_STACK_H_