[DECNET]: Fix input routing bug

This patch fixes a silly bug that has been in the input routing code
for some time. It results in trying to send to a node directly when
the origin of the packet is via the default router.

Its been tested by Alan Kemmerer <alan.kemmerer@mittalsteel.com> who
reported the bug and its a fairly obvious fix for a typo.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Patrick Caulfield <patrick@tykepenguin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>