netlink: add netlink_dump_control structure for netlink_dump_start()

Davem considers that the argument list of this interface is getting
out of control. This patch tries to address this issue following
his proposal:

struct netlink_dump_control c = { .dump = dump, .done = done, ... };

netlink_dump_start(..., &c);

Suggested by David S. Miller.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/infiniband/core/netlink.c b/drivers/infiniband/core/netlink.c
index d1c8196..396e293 100644
--- a/drivers/infiniband/core/netlink.c
+++ b/drivers/infiniband/core/netlink.c
@@ -147,9 +147,13 @@
 			if (op < 0 || op >= client->nops ||
 			    !client->cb_table[RDMA_NL_GET_OP(op)].dump)
 				return -EINVAL;
-			return netlink_dump_start(nls, skb, nlh,
-						  client->cb_table[op].dump,
-						  NULL, 0);
+
+			{
+				struct netlink_dump_control c = {
+					.dump = client->cb_table[op].dump,
+				};
+				return netlink_dump_start(nls, skb, nlh, &c);
+			}
 		}
 	}