ldap_server: Terminate LDAP connections on krb ticket expiry

ldap_server: Terminate LDAP connections on krb ticket expiry

See RFC4511 section 4.4.1 and

https://lists.samba.org/archive/cifs-protocol/2020-August/003515.html

for details: Windows terminates LDAP connections when the krb5 ticket
expires, Samba should do the same. This patch slightly deviates from
Windows behaviour by sending a LDAP exop response with msgid 0 that is
ASN1-encoded conforming to RFC4511.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=14465

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
(cherry picked from commit eb72f887b0bf91c050fd5d911f58a1b3ff9b8bcc)