Support for EC curve Hello extension, EC curve fallback

src/libtls/tls_crypto.h

@@ -395,6 +395,13 @@ struct tls_crypto_t {
 	 */
 	void (*get_signature_algorithms)(tls_crypto_t *this, tls_writer_t *writer);
 
+	/**
+	 * Write the list of supported elliptic curves to writer.
+	 *
+	 * @param writer		writer to write elliptic curves to
+	 */
+	void (*get_curves)(tls_crypto_t *this, tls_writer_t *writer);
+
 	/**
 	 * Set the protection layer of the TLS stack to control it.
 	 *