pkt_sched: add DRR scheduler

Add classful DRR scheduler as a more flexible replacement for SFQ.

The main difference to the algorithm described in "Efficient Fair Queueing
using Deficit Round Robin" is that this implementation doesn't drop packets
from the longest queue on overrun because its classful and limits are
handled by each individual child qdisc.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/pkt_sched.h

@@ -500,4 +500,20 @@ struct tc_netem_corrupt
 
 #define NETEM_DIST_SCALE	8192
 
+/* DRR */
+
+enum
+{
+	TCA_DRR_UNSPEC,
+	TCA_DRR_QUANTUM,
+	__TCA_DRR_MAX
+};
+
+#define TCA_DRR_MAX	(__TCA_DRR_MAX - 1)
+
+struct tc_drr_stats
+{
+	u32	deficit;
+};
+
 #endif