bql: Byte queue limits

Networking stack support for byte queue limits, uses dynamic queue
limits library.  Byte queue limits are maintained per transmit queue,
and a dql structure has been added to netdev_queue structure for this
purpose.

Configuration of bql is in the tx-<n> sysfs directory for the queue
under the byte_queue_limits directory.  Configuration includes:
limit_min, bql minimum limit
limit_max, bql maximum limit
hold_time, bql slack hold time

Also under the directory are:
limit, current byte limit
inflight, current number of bytes on the queue

Signed-off-by: Tom Herbert <therbert@google.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/Kconfig b/net/Kconfig
index 63d2c5d..2d99873 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -239,6 +239,12 @@
 	  Cgroup subsystem for use in assigning processes to network priorities on
 	  a per-interface basis
 
+config BQL
+	boolean
+	depends on SYSFS
+	select DQL
+	default y
+
 config HAVE_BPF_JIT
 	bool