s3:messages: allow messaging_filtered_read_send() to use wrapper tevent_context
As it gets 'messaging_context' as argument, we're sure a messaging context
with a raw tevent context already exist.
It means we can allow a wrapper tevent context that wrapps the main tevent
context of the messaging context.
The use of tevent_req_defer_callback() makes sure that the callers
callback function calls messaging_filtered_read_recv() from the
correct "wrapped" environment.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>