[DECNET]: Remove some redundant ifdeffed code

Signed-off-by: Patrick Caulfield <patrick@tykepenguin.com>
Signed-off-by: Steven Whitehouse <steve@chygwyn.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>