[media] dvb-net: split the logic at dvb_net_ule() into other functions

This function is too big and too complex, making really hard
to understand what's there.

Split it into sub-routines, in order to make it easier to be
understood, and to allow gcc to better parse it.

As a bonus, it gets rid of a goto in the middle of a routine.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>