bridge: fix potential crash in __netdev_pick_tx()

Commit c29390c6 ("xps: must clear sender_cpu before forwarding")
fixed an issue in normal forward path, caused by sender_cpu & napi_id
skb fields being an union.

Bridge is another point where skb can be forwarded, so we need
the same cure.

Bug triggers if packet was received on a NIC using skb_mark_napi_id()

Fixes: 2bd82484 ("xps: fix xps for stacked devices")
Signed-off-by: NEric Dumazet <edumazet@google.com>
Reported-by: NBob Liu <bob.liu@oracle.com>
Tested-by: NBob Liu <bob.liu@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br_forward.c

@@ -42,6 +42,7 @@ int br_dev_queue_push_xmit(struct sock *sk, struct sk_buff *skb)
 	} else {
 		skb_push(skb, ETH_HLEN);
 		br_drop_fake_rtable(skb);
+		skb_sender_cpu_clear(skb);
 		dev_queue_xmit(skb);
 	}