V4L/DVB (11561): Siano: add messages handling for big-endian target

Add code that modify the content of Siano's protocol
messages when running with big-endian target.

Signed-off-by: Uri Shkolnik <uris@siano-ms.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>