[IPV4]: Cleanup call to __neigh_lookup()

Back in the times of Linux 2.2, negative values for the creat parameter
of __neigh_lookup() had a particular meaning, but no longer, so we
should pass 1 instead.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: David S. Miller <davem@davemloft.net>