Rename ssl_set_bio_timeout() to set_bio()

Initially thought it was best to keep the old function around and add a new
one, but this so many ssl_set_xxx() functions are changing anyway...
diff --git a/programs/ssl/ssl_mail_client.c b/programs/ssl/ssl_mail_client.c
index 84ae22e..db51399 100644
--- a/programs/ssl/ssl_mail_client.c
+++ b/programs/ssl/ssl_mail_client.c
@@ -606,7 +606,7 @@
 
     mbedtls_ssl_set_rng( &ssl, mbedtls_ctr_drbg_random, &ctr_drbg );
     mbedtls_ssl_set_dbg( &conf, my_debug, stdout );
-    mbedtls_ssl_set_bio_timeout( &ssl, &server_fd, mbedtls_net_send, mbedtls_net_recv, NULL );
+    mbedtls_ssl_set_bio( &ssl, &server_fd, mbedtls_net_send, mbedtls_net_recv, NULL );
 
     if( opt.force_ciphersuite[0] != DFL_FORCE_CIPHER )
         mbedtls_ssl_set_ciphersuites( &conf, opt.force_ciphersuite );