RDMA/cma: Use neigh_event_send() to start neighbour discovery

Calling arp_send() to initiate neighbour discovery (ND) doesn't do the
full ND protocol.  Namely, it doesn't handle retransmitting the arp
request if it is dropped. The function neigh_event_send() does all
this.  Without doing full ND, RDMA address resolution fails in the
presence of dropped ARP broadcast packets.
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Acked-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/core/addr.c

@@ -161,8 +161,7 @@ static void addr_send_arp(struct sockaddr_in *dst_in)
 	if (ip_route_output_key(&rt, &fl))
 		return;
 
-	arp_send(ARPOP_REQUEST, ETH_P_ARP, rt->rt_gateway, rt->idev->dev,
-		 rt->rt_src, NULL, rt->idev->dev->dev_addr, NULL);
+	neigh_event_send(rt->u.dst.neighbour, NULL);
 	ip_rt_put(rt);
 }