ipvs: fix ARP resolving for direct routing mode

After the change "Make neigh lookups directly in output packet path"
(commit a263b309) IPVS can not reach the real server for DR mode
because we resolve the destination address from IP header, not from
route neighbour. Use the new FLOWI_FLAG_KNOWN_NH flag to request
output routes with known nexthop, so that it has preference
on resolving.
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netfilter/ipvs/ip_vs_xmit.c

@@ -50,6 +50,7 @@ enum {
 				      * local
 				      */
 	IP_VS_RT_MODE_CONNECT	= 8, /* Always bind route to saddr */
+	IP_VS_RT_MODE_KNOWN_NH	= 16,/* Route via remote addr */
 };
 
 /*
@@ -113,6 +114,8 @@ static struct rtable *do_output_route4(struct net *net, __be32 daddr,
 	fl4.daddr = daddr;
 	fl4.saddr = (rt_mode & IP_VS_RT_MODE_CONNECT) ? *saddr : 0;
 	fl4.flowi4_tos = rtos;
+	fl4.flowi4_flags = (rt_mode & IP_VS_RT_MODE_KNOWN_NH) ?
+			   FLOWI_FLAG_KNOWN_NH : 0;
 
 retry:
 	rt = ip_route_output_key(net, &fl4);
@@ -1061,7 +1064,8 @@ ip_vs_dr_xmit(struct sk_buff *skb, struct ip_vs_conn *cp,
 	if (!(rt = __ip_vs_get_out_rt(skb, cp->dest, cp->daddr.ip,
 				      RT_TOS(iph->tos),
 				      IP_VS_RT_MODE_LOCAL |
-					IP_VS_RT_MODE_NON_LOCAL, NULL)))
+				      IP_VS_RT_MODE_NON_LOCAL |
+				      IP_VS_RT_MODE_KNOWN_NH, NULL)))
 		goto tx_error_icmp;
 	if (rt->rt_flags & RTCF_LOCAL) {
 		ip_rt_put(rt);