[media] dvb_usb_v2: rework USB streaming logic

Control flow order changed a little bit. HW PID filter is now
disabled also when streaming is stopped - earlier it was just
set only when streaming was started.
Control flow is now:
* set streaming status bit
* submit USB streaming packets
* enable HW PID filter
* ask device to start streaming
* N x add PID to device HW PID filter
... streaming video ...
* N x remove PID from device HW PID filter
* ask device to stop streaming
* disable HW PID filter
* kill USB streaming packets
* clear streaming status bit

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>