sips: fix send ack

send ack message was queued in a queue unstacked in
the main thread, but this last is busy by application
waiting for the ack... deadloop!
This patch fixes this by calling the application ack
confirmation callback immediatly when the TLS acknowledge
the ack.

Change-Id: Ic8fe6102acca184d78f86e3e8524382e9b257f4b
Tuleap: #433