Add TCP auto read callback API.

Change-Id: I913b274c790192d84aba0a26f58e8a625f772e71
diff --git a/mbtk/mbtk_lib/src/mbtk_tcpip_at.c b/mbtk/mbtk_lib/src/mbtk_tcpip_at.c
index 8c1003a..ccfe1ad 100755
--- a/mbtk/mbtk_lib/src/mbtk_tcpip_at.c
+++ b/mbtk/mbtk_lib/src/mbtk_tcpip_at.c
@@ -638,3 +638,16 @@
     return 0;
 }
 
+/*
+* Set socket auto read callback function,NULL for close auto read.
+*/
+void mbtk_tcpip_set_read_cb(int link_id, mbtk_tcpip_read_callback_func read_cb)
+{
+    if(!tcpip_link_check(link_id)) {
+        LOGE("Link error.");
+        return;
+    }
+
+    tcpip_link[link_id].tcpip_info.cli_info.read_cb = read_cb;
+}
+