[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>

net/ipv4/arp.c

@@ -835,9 +835,8 @@ static int arp_process(struct sk_buff *skb)
 			}
 			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);

net/ipv4/route.c

@@ -1768,7 +1768,7 @@ static inline int __mkroute_input(struct sk_buff *skb,
 	if (err)
 		flags |= RTCF_DIRECTSRC;
 
-	if (out_dev == in_dev && err && !(flags & (RTCF_NAT | RTCF_MASQ)) &&
+	if (out_dev == in_dev && err && !(flags & RTCF_MASQ) &&
 	    (IN_DEV_SHARED_MEDIA(out_dev) ||
 	     inet_addr_onlink(out_dev, saddr, FIB_RES_GW(*res))))
 		flags |= RTCF_DOREDIRECT;
@@ -1777,7 +1777,7 @@ static inline int __mkroute_input(struct sk_buff *skb,
 		/* Not IP (i.e. ARP). Do not create route, if it is
 		 * invalid for proxy arp. DNAT routes are always valid.
 		 */
-		if (out_dev == in_dev && !(flags & RTCF_DNAT)) {
+		if (out_dev == in_dev) {
 			err = -EINVAL;
 			goto cleanup;
 		}