V4L/DVB (11091): cx18, ivtv: Ensure endianess for linemasks in VBI embedded in MPEG stream

The sliced VBI payloads that cx18 and ivtv would insert in the MPEG stream
did not have consistent endianess for the linemasks in the payload (a big
endian platform would write them out big endian).  This change ensures the
linemasks are always stored as little-endian in the MPEG stream to ensure
cross platform consistency in parsing the generated MPEG stream.

Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>