Restructure ssl_handshake_init() and small fixes

include/polarssl/ssl.h

@@ -1682,6 +1682,13 @@ int ssl_close_notify( ssl_context *ssl );
  */
 void ssl_free( ssl_context *ssl );
 
+/**
+ * \brief          Initialize SSL session structure
+ *
+ * \param session  SSL session
+ */
+void ssl_session_init( ssl_session *session );
+
 /**
  * \brief          Free referenced items in an SSL session including the
  *                 peer certificate and clear memory