s3: Properly deal with exited winbind children

s3: Properly deal with exited winbind children

When a winbind child exits, we need to immediately close the socket. If not,
the next request to that child will be sent to a socket without a listener,
leading to a failed request. This failed request will then trigger a proper
re-init.

This patch avoids the one failed request.

Autobuild-User: Volker Lendecke <vlendec@samba.org>
Autobuild-Date: Wed May  4 13:32:16 CEST 2011 on sn-devel-104