net-tc: convert tc_verd to integer bitfields

Extract the remaining two fields from tc_verd and remove the __u16
completely. TC_AT and TC_FROM are converted to equivalent two-bit
integer fields tc_at and tc_from. Where possible, use existing
helper skb_at_tc_ingress when reading tc_at. Introduce helper
skb_reset_tc to clear fields.

Not documenting tc_from and tc_at, because they will be replaced
with single bit fields in follow-on patches.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -599,7 +599,6 @@ static inline bool skb_mstamp_after(const struct skb_mstamp *t1,
  *	@nf_bridge: Saved data about a bridged frame - see br_netfilter.c
  *	@skb_iif: ifindex of device we arrived on
  *	@tc_index: Traffic control index
- *	@tc_verd: traffic control verdict
  *	@hash: the packet hash
  *	@queue_mapping: Queue mapping for multiqueue devices
  *	@xmit_more: More SKBs are pending for this queue
@@ -752,13 +751,12 @@ struct sk_buff {
 #endif
 #ifdef CONFIG_NET_CLS_ACT
 	__u8			tc_skip_classify:1;
+	__u8			tc_at:2;
+	__u8			tc_from:2;
 #endif
 
 #ifdef CONFIG_NET_SCHED
 	__u16			tc_index;	/* traffic control index */
-#ifdef CONFIG_NET_CLS_ACT
-	__u16			tc_verd;	/* traffic control verdict */
-#endif
 #endif
 
 	union {