Fix code warning.

Change-Id: Ib11fb49f528d3688351ae349d5b4e307c28b3967
diff --git a/mbtk/libmbtk_lib_v2/net/mbtk_sock2.c b/mbtk/libmbtk_lib_v2/net/mbtk_sock2.c
index ae5329e..2b508a5 100755
--- a/mbtk/libmbtk_lib_v2/net/mbtk_sock2.c
+++ b/mbtk/libmbtk_lib_v2/net/mbtk_sock2.c
@@ -919,7 +919,7 @@
 }
 
 extern int mbtk_sock_write(mbtk_sock_handle handle,mbtk_sock_session session,
-                void *buffer,
+                const void *buffer,
                 unsigned int buf_len,
                 unsigned int timeout,
                 int *mbtk_errno)