ui: extend VNC trottling tracing to SASL codepaths

In previous commit:

  commit 6aa22a29
  Author: Daniel P. Berrange <berrange@redhat.com>
  Date:   Mon Dec 18 19:12:27 2017 +0000

    ui: add trace events related to VNC client throttling

trace points related to unthrottling client I/O were missed from the
SASL codepaths.

Reported-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Message-id: 20180205114938.15784-5-berrange@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>