DECnet was removed by commit 1202cdd6 ("Remove DECnet support from
kernel"). Let's also revome its flow structure.

Compile-tested only (allmodconfig).
Signed-off-by: NGuillaume Nault <gnault@redhat.com>
Acked-by: NStephen Hemminger <stephen@networkplumber.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>