net: restore gnet_stats_basic to previous definition

In 5e140dfc1fe87eae27846f193086724806b33c7d "net: reorder struct Qdisc
for better SMP performance" the definition of struct gnet_stats_basic
changed incompatibly, as copies of this struct are shipped to
userland via netlink.

Restoring old behavior is not welcome, for performance reason.

Fix is to use a private structure for kernel, and
teach gnet_stats_copy_basic() to convert from kernel to user land,
using legacy structure (struct gnet_stats_basic)

Based on a report and initial patch from Michael Spang.

Reported-by: Michael Spang <mspang@csclub.uwaterloo.ca>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
index 7597fe1..12b2fb04 100644
--- a/net/sched/sch_drr.c
+++ b/net/sched/sch_drr.c
@@ -22,7 +22,7 @@
 	unsigned int			refcnt;
 	unsigned int			filter_cnt;
 
-	struct gnet_stats_basic		bstats;
+	struct gnet_stats_basic_packed		bstats;
 	struct gnet_stats_queue		qstats;
 	struct gnet_stats_rate_est	rate_est;
 	struct list_head		alist;