BugLink: http://bugs.launchpad.net/bugs/1670508

Allow to decrypt transformed packets that are bigger than the big
buffer size. In particular it is used for read responses that can
only exceed the big buffer size.
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
(cherry picked from commit c42a6abe)
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>