kdc: add enable_fast option (enabled by default)

This makes it possible to disable fast if needed,
which is very good for regression tests.
Samba disables this in a few test environments with this
option.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15002
BUG: https://bugzilla.samba.org/show_bug.cgi?id=15005

Signed-off-by: Stefan Metzmacher <metze@samba.org>

kdc/fast.c

@@ -756,6 +756,9 @@ _kdc_fast_unwrap_request(astgs_request_t r,
     const PA_DATA *pa;
     int i = 0;
 
+    if (!r->config->enable_fast)
+	return 0;
+
     ret = fast_unwrap_request(r, tgs_ticket, tgs_ac);
     if (ret)
 	return ret;