First part of fix for bug #7159 - client rpc_transport doesn't cope with bad server...

First part of fix for bug #7159 - client rpc_transport doesn't cope with bad server data returns.

Ensure that subreq is *always* talloc_free'd in the _done
function, as it has an event timeout attached. If the
read requests look longer than the cli->timeout, then
the timeout fn is called with already freed data.

Jeremy.
(cherry picked from commit ad77ae1d5870e06f8587ecf634e0b6bdcbb950d7)
(similar to commit 6e5b6b5acb30869eb63b25ed1406014101a5e89d)

Signed-off-by: Stefan Metzmacher <metze@samba.org>