Fix polarssl

Change-Id: I4b461ce72f7e828c689f1190dec78bea40f60d50
diff --git a/mbtk/mbtk_lib/inc/mbtk_sock_internal.h b/mbtk/mbtk_lib/inc/mbtk_sock_internal.h
index e0cbaa0..4ee7125 100755
--- a/mbtk/mbtk_lib/inc/mbtk_sock_internal.h
+++ b/mbtk/mbtk_lib/inc/mbtk_sock_internal.h
@@ -9,6 +9,7 @@
 typedef struct {
     int fd;
     mbtk_sock_type type; // socket type:TCP or UDP
+#ifdef MBTK_POLARSSL_SUPPORT
     entropy_context* entropy;
     ctr_drbg_context* ctr_drbg;
     ssl_context *ssl;
@@ -16,6 +17,7 @@
     x509_crt *cacert;
     x509_crt *clicert;
     pk_context* pkey;
+#endif
 } mbtk_sock_inter_info_s;
 
 typedef struct {