[NETLINK]: cleanup unused macro in net/netlink/af_netlink.c

1 line removal, of unused macro.
ran 'egrep -r' from linux-2.6.16/ for Nprintk and
didn't see it anywhere else but here, in #define...

Signed-off-by: Soyoung Park <speattle@yahoo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>