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_pthread_server.c b/programs/ssl/ssl_pthread_server.c
index 7e576d4..cbe6b4d 100644
--- a/programs/ssl/ssl_pthread_server.c
+++ b/programs/ssl/ssl_pthread_server.c
@@ -197,7 +197,7 @@
 
     mbedtls_printf( "  [ #%d ]  ok\n", thread_id );
 
-    mbedtls_ssl_set_bio_timeout( &ssl, &client_fd, mbedtls_net_send, mbedtls_net_recv, NULL );
+    mbedtls_ssl_set_bio( &ssl, &client_fd, mbedtls_net_send, mbedtls_net_recv, NULL );
 
     mbedtls_printf( "  [ #%d ]  ok\n", thread_id );