[media] dvb_net: prepare to split a very complex function

The dvb_net code has a really complex function, meant to handle
DVB network packages: it is long, has several loops and ifs
inside, and even cause warnings with gcc5.

Prepare it to be split into smaller functions by storing all
arguments and internal vars inside a struct.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>