Orphan DECnet

Due to lack of time, space, motivation, hardware and probably expertise,
I have reluctantly decided to orphan the DECnet code in the kernel.

Judging by the deafening silence on the linux-decnet mailing list I
suspect it's either not being used anyway, or the few people that are
using it are happy with their older kernels.

Signed-off-by: Christine Caulfield <christine.caulfield@googlemail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>