[IPV4]: Remove unsupported DNAT (RTCF_NAT and RTCF_NAT) in IPV4

- The DNAT (Destination NAT) is not implemented in IPV4.

- This patch remove the code which checks these flags
in net/ipv4/arp.c and net/ipv4/route.c.

The RTCF_NAT and RTCF_NAT should stay in the header (linux/in_route.h)
because they are used in DECnet.

Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 9eb6d3a..46edf1c 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -835,9 +835,8 @@
 			}
 			goto out;
 		} else if (IN_DEV_FORWARD(in_dev)) {
-			if ((rt->rt_flags&RTCF_DNAT) ||
-			    (addr_type == RTN_UNICAST  && rt->u.dst.dev != dev &&
-			     (arp_fwd_proxy(in_dev, rt) || pneigh_lookup(&arp_tbl, &init_net, &tip, dev, 0)))) {
+			    if (addr_type == RTN_UNICAST  && rt->u.dst.dev != dev &&
+			     (arp_fwd_proxy(in_dev, rt) || pneigh_lookup(&arp_tbl, &init_net, &tip, dev, 0))) {
 				n = neigh_event_ns(&arp_tbl, sha, &sip, dev);
 				if (n)
 					neigh_release(n);