Some style and documentation fixes
1. Change description of of hte `MBEDTLS_ECP_RESTARTABLE`
in the configuration file.
2. Change check for compilation of `rs_ctx` to positive flow.
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index c594b69..950319a 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -695,8 +695,9 @@
*
* Uncomment this macro to enable restartable ECC computations.
*
- * \note MBEDTLS_ECP_RESTARTABLE cannot be defined if there is an alternative
- * implementation for one of the ECP, ECDSA or ECDH functions. *
+ * \note This option only works with the default software implementation of
+ * elliptic curve functionality. It is incompatible with
+ * MBEDTLS_ECP_ALT, MBEDTLS_ECDH_xxx_ALT and MBEDTLS_ECDSA_xxx_ALT.
*/
//#define MBEDTLS_ECP_RESTARTABLE