V4L/DVB (3966): Core: ULE fixes and RFC4326 additions

Fix some problems regarding support for Unidirectional Lightweight
Encapsulation (ULE) in dvbnet.c.
The original ULE code was based on a draft.  In the meantime, ULE has been
published in RFC 4326 (ftp://ftp.rfc-editor.org/in-notes/rfc4326.txt).
With these fixes, and some additions (which are included in the patch), the
decaps code should now be complient to RFC4326.

Signed-off-by: Christian Praehauser <cpraehaus@cosy.sbg.ac.at>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>