add socket wrapper for at framework

you can use at framework to send/recv data in socket API
example: see examples\tcp_through_module_based_at_socket
project: see board\TencentOS_tiny_EVB_MX_Plus\KEIL\tcp_through_module_based_at_socket

net/socket_wrapper/include/tos_at_socket_prv.h

@@ -0,0 +1,60 @@
+/*----------------------------------------------------------------------------
+ * Tencent is pleased to support the open source community by making TencentOS
+ * available.
+ *
+ * Copyright (C) 2019 THL A29 Limited, a Tencent company. All rights reserved.
+ * If you have downloaded a copy of the TencentOS binary from Tencent, please
+ * note that the TencentOS binary is licensed under the BSD 3-Clause License.
+ *
+ * If you have downloaded a copy of the TencentOS source code from Tencent,
+ * please note that TencentOS source code is licensed under the BSD 3-Clause
+ * License, except for the third-party components listed below which are
+ * subject to different license terms. Your integration of TencentOS into your
+ * own projects may require compliance with the BSD 3-Clause License, as well
+ * as the other licenses applicable to the third-party components included
+ * within TencentOS.
+ *---------------------------------------------------------------------------*/
+
+#ifndef  _TOS_AT_SOCKET_PRV_H_
+#define  _TOS_AT_SOCKET_PRV_H_
+
+#include "sal_module_wrapper.h"
+
+#define SOCKET_CTL_MAX      6 /* should consistent with AT_DATA_CHANNEL_NUM */
+
+typedef struct socket_control_st {
+    int             fd;         /* the real channel id allocated by at framework.
+                                    for some module like NBIot(bc35), you only know the channel id until you really do the
+                                    connect to the server */
+    int             is_taken;   /* is this control usable?(if is_taken is FALSE then it's not usable) */
+
+    sal_proto_t     protocol;
+} socket_ctl_t;
+
+int socket_id_sanity_check(int id);
+
+int socket_id_set_sanity_check(int id);
+
+int socket_id_alloc(void);
+
+void socket_id_free(int id);
+
+void socket_set_protocol(int id, sal_proto_t protocol);
+
+sal_proto_t socket_get_protocol(int id);
+
+void socket_set_fd(int id, int fd);
+
+int socket_get_fd(int id);
+
+#define SOCKET_ID_SANITY_CHECK(id)          \
+    if (!socket_id_sanity_check(id)) {      \
+        return -1;                          \
+    }
+
+#define SOCKET_ID_SET_SANITY_CHECK(id)          \
+    if (!socket_id_set_sanity_check(id)) {      \
+        return -1;                              \
+    }
+
+#endif /* _TOS_AT_SOCKET_PRV_H_ */