Document the new BIO functions introduced as part of the size_t work

Reviewed-by: Richard Levitte <levitte@openssl.org>
diff --git a/doc/man3/BIO_f_ssl.pod b/doc/man3/BIO_f_ssl.pod
index 3f9635e..48bc150 100644
--- a/doc/man3/BIO_f_ssl.pod
+++ b/doc/man3/BIO_f_ssl.pod
@@ -108,7 +108,7 @@
 SSL BIOs are exceptional in that if the underlying transport
 is non blocking they can still request a retry in exceptional
 circumstances. Specifically this will happen if a session
-renegotiation takes place during a BIO_read() operation, one
+renegotiation takes place during a BIO_read_ex() operation, one
 case where this happens is when step up occurs.
 
 The SSL flag SSL_AUTO_RETRY can be