bridge: initialize fake_rtable metrics

bridge netfilter code uses a fake_rtable, and we must init its _metric
field or risk NULL dereference later.

Ref: https://bugzilla.kernel.org/show_bug.cgi?id=35672

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_netfilter.c

@@ -117,6 +117,10 @@ static struct dst_ops fake_dst_ops = {
  * ipt_REJECT needs it.  Future netfilter modules might
  * require us to fill additional fields.
  */
+static const u32 br_dst_default_metrics[RTAX_MAX] = {
+	[RTAX_MTU - 1] = 1500,
+};
+
 void br_netfilter_rtable_init(struct net_bridge *br)
 {
 	struct rtable *rt = &br->fake_rtable;
@@ -124,7 +128,7 @@ void br_netfilter_rtable_init(struct net_bridge *br)
 	atomic_set(&rt->dst.__refcnt, 1);
 	rt->dst.dev = br->dev;
 	rt->dst.path = &rt->dst;
-	dst_metric_set(&rt->dst, RTAX_MTU, 1500);
+	dst_init_metrics(&rt->dst, br_dst_default_metrics, true);
 	rt->dst.flags	= DST_NOXFRM;
 	rt->dst.ops = &fake_dst_ops;
 }