net_sched fix: reclassification needs to consider ether protocol changes

actions could change the etherproto in particular with ethernet
tunnelled data. Typically such actions, after peeling the outer header,
will ask for the packet to be  reclassified. We then need to restart
the classification with the new proto header.

Example setup used to catch this:
sudo tc qdisc add dev $ETH ingress
sudo $TC filter add dev $ETH parent ffff: pref 1 protocol 802.1Q \
u32 match u32 0 0 flowid 1:1 \
action  vlan pop reclassify

Fixes: 3b3ae88 ("net: sched: consolidate tc_classify{,_compat}")
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_api.c

@@ -1852,6 +1852,7 @@ int tc_classify(struct sk_buff *skb, const struct tcf_proto *tp,
 	}
 
 	tp = old_tp;
+	protocol = tc_skb_protocol(skb);
 	goto reclassify;
 #endif
 }