fixed a fd leak when trying to regain contact to a domain controller

fixed a fd leak when trying to regain contact to a domain controller
in winbind

When a w2k3 DC is rebooted the 139/445 ports come up before the
udp/389 cldap port. During this brief period, winbind manages to
connect to 139/445 but not to udp 389. It then enters a tight loop
where it leaks one fd each time. In a couple of seconds it runs out of
file descriptors, and leaves winbind crippled after the DC does
finally come up
(cherry picked from commit 57187cafbcc053e75bb54750494df9feabe3a738)