The DRX-K doesn't change the delivery system at set_properties,
but do it at frontend init. This causes problems on programs like
w_scan that, by default, opens both frontends.

Instead, explicitly set the format when set_parameters callback is
called.
Tested-by: Eddi De Pieri <eddi@depieri.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>