s3: smbd: Fix memory leak in smbd_server_connection_terminate_done().

The function smbd_server_connection_terminate_done() does not free subreq
which is allocated in smbXsrv_connection_shutdown_send, this can be a
memory leakage if multi-channel is enabled.

Suggested fix by haihua yang <hhyangdev@gmail.com>

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15174

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Noel Power <noel.power@suse.com>

Autobuild-User(master): Noel Power <npower@samba.org>
Autobuild-Date(master): Fri Sep 23 09:51:20 UTC 2022 on sn-devel-184
