s4:auth: Fix 'no delegation' logic in gensec_gssapi_start()

s4:auth: Fix 'no delegation' logic in gensec_gssapi_start()

This fixes samba4.ntvfs.cifs.krb5.base.lock test with MIT Kerberos.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15912

Signed-off-by: Andreas Schneider <asn@samba.org>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>

Reviewed-by: Alexander Bokovoy <ab@samba.org>
(cherry picked from commit 66d3e5e49d34b0a4bfb8f2c862d48d11e27b2ea2)

Autobuild-User(v4-23-test): Jule Anger <janger@samba.org>
Autobuild-Date(v4-23-test): Fri Sep 12 07:23:04 UTC 2025 on atb-devel-224