feat(esp8266): Add WIFI socket and async APIs

1. add section to linking file

components/esp8266/include/esp_aio.h

@@ -0,0 +1,64 @@
+// Copyright 2018 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_AIO_H
+#define _ESP_AIO_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * declare
+ */
+struct esp_aio;
+
+/*
+ * aio callback function type
+ */
+typedef int (*esp_aio_cb_t)(struct esp_aio *aio);
+
+/*
+ * aio data object
+ */
+typedef struct esp_aio {
+    int             fd;     // file description
+
+    const char      *pbuf;  // send/recv data pointer
+    size_t          len;    // buffer length by bytes
+
+    esp_aio_cb_t    cb;     // callback function
+    void            *arg;   // user callback function private data
+
+    int             ret;    // asynchronous operation result
+} esp_aio_t;
+
+/*
+ * aio data object
+ */
+typedef struct esp_aio_data {
+    const char      *pbuf;  // send/recv data pointer
+    size_t          len;    // buffer length by bytes
+
+    int             status; // lowlevel data status
+} esp_aio_data_t;
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _ESP_AIO_H */