CVE-2016-2125: s4:gensec_gssapi: don't use GSS_C_DELEG_FLAG by default

CVE-2016-2125: s4:gensec_gssapi: don't use GSS_C_DELEG_FLAG by default

This disabled the usage of GSS_C_DELEG_FLAG by default, as
GSS_C_DELEG_POLICY_FLAG is still used by default we let the
KDC decide if we should send delegated credentials to a remote server.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12445

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Alexander Bokovoy <ab@samba.org>
Reviewed-by: Simo Sorce <idra@samba.org>