[media] gspca - sonixj: Update the JPEG quality for best image transfer

During image capture, the filling rate of the isoc packets is computed.
It is then used by a work queue to update the current JPEG quality.

Tested-by: Franck Bourdonnec <fbourdonnec@chez.com>
Signed-off-by: Jean-François Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>