tldap: Centralize connection rundown on error

tldap: Centralize connection rundown on error

Whenever send or recv return -1, we have to cancel all pending
requests and our transport stream is no longer usable: Discard it upon
such an error.

To avoid duplicate state, tldap_connection_ok() now looks at whether
we have a tstream_context around.

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 f745f5b12560dbcb7be6f3ffb3bc10704c87149c)