[IPv4]: Reply net unreachable ICMP message

IPv4 stack doesn't reply any ICMP destination unreachable message
with net unreachable code when IP detagrams are being discarded
because of no route could be found in the forwarding path.
Incidentally, IPv6 stack replies such ICMPv6 message in the similar
situation.
Signed-off-by: Mitsuru Chinen <mitch@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/route.c

@@ -1252,6 +1252,7 @@ static int ip_error(struct sk_buff *skb)
 			break;
 		case ENETUNREACH:
 			code = ICMP_NET_UNREACH;
+			IP_INC_STATS_BH(IPSTATS_MIB_INNOROUTES);
 			break;
 		case EACCES:
 			code = ICMP_PKT_FILTERED;
@@ -1881,6 +1882,8 @@ no_route:
 	RT_CACHE_STAT_INC(in_no_route);
 	spec_dst = inet_select_addr(dev, 0, RT_SCOPE_UNIVERSE);
 	res.type = RTN_UNREACHABLE;
+	if (err == -ESRCH)
+		err = -ENETUNREACH;
 	goto local_input;
 
 	/*