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/tcpip_adapter/include/tcpip_adapter_compatible/tcpip_adapter_compat.h

@@ -0,0 +1,40 @@
+// 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 _TCPIP_ADAPTER_COMPAT_H_
+#define _TCPIP_ADAPTER_COMPAT_H_
+
+/**
+ * @brief This function is called from wifi_init to assure backward compatibility mode
+ * of tcpip_adapter. In case of legacy use, default instances of ap and sta
+ * are created and handlers are registered
+ *
+ * @note This api is given in a separate header, which is included internally (from wifi driver)
+ * rather then user initialization code.
+ *
+ * @return ESP_OK on success
+ */
+esp_err_t tcpip_adapter_set_default_wifi_handlers(void);
+
+/**
+ * @brief This function is called from ethernet driver init code to facilitate
+ * autostart fo the driver in backward compatible tcpip_adapter way
+ *
+ * @param[in] h Handle to the ethernet driver
+ *
+ * @return ESP_OK on success
+ */
+esp_err_t tcpip_adapter_start_eth(void* h);
+
+#endif //_TCPIP_ADAPTER_COMPAT_H_