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>

net/sched/sch_netem.c

@@ -626,7 +626,7 @@ deliver:
 			 * If it's at ingress let's pretend the delay is
 			 * from the network (tstamp will be updated).
 			 */
-			if (G_TC_FROM(skb->tc_verd) & AT_INGRESS)
+			if (skb->tc_from & AT_INGRESS)
 				skb->tstamp = 0;
 #endif