V4L/DVB (12511): V4L2: add a new V4L2_CID_BAND_STOP_FILTER integer control

Add a new V4L2_CID_BAND_STOP_FILTER integer control, which either switches the
band-stop filter off, or sets it to a certain strength.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>