s4:ldap_server: let ldapsrv_call_writev_start use conn_idle_time to limit the time

s4:ldap_server: let ldapsrv_call_writev_start use conn_idle_time to limit the time

If the client is not able to receive the results within connections idle
time, then we should treat it as dead. It's value is 15 minutes (900 s)
by default.

In order to limit that further an admin can use 'socket options'
and set TCP_KEEPCNT, TCP_KEEPIDLE, TCP_KEEPINTVL and/or TCP_USER_TIMEOUT
to useful values.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15202

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Wed Oct 19 17:13:39 UTC 2022 on sn-devel-184