mlx4 stats are chaotic because a deferred work queue is responsible
to update them every 250 ms.

Even sampling stats every one second with "sar -n DEV 1" gives
variations like the following :

lpaa23:~# sar -n DEV 1 10 | grep eth0 | cut -c1-65
07:39:22         eth0 146877.00 3265554.00   9467.15 4828168.50
07:39:23         eth0 146587.00 3260329.00   9448.15 4820445.98
07:39:24         eth0 146894.00 3259989.00   9468.55 4819943.26
07:39:25         eth0 110368.00 2454497.00   7113.95 3629012.17  <<>>
07:39:26         eth0 146563.00 3257502.00   9447.25 4816266.23
07:39:27         eth0 145678.00 3258292.00   9389.79 4817414.39
07:39:28         eth0 145268.00 3253171.00   9363.85 4809852.46
07:39:29         eth0 146439.00 3262185.00   9438.97 4823172.48
07:39:30         eth0 146758.00 3264175.00   9459.94 4826124.13
07:39:31         eth0 146843.00 3256903.00   9465.44 4815381.97
Average:         eth0 142827.50 3179259.70   9206.30 4700578.16

This patch allows rx/tx bytes/packets counters being folded at the
time we need stats.

We now can fetch stats every 1 ms if we want to check NIC behavior
on a small time window. It is also easier to detect anomalies.

lpaa23:~# sar -n DEV 1 10 | grep eth0 | cut -c1-65
07:42:50         eth0 142915.00 3177696.00   9212.06 4698270.42
07:42:51         eth0 143741.00 3200232.00   9265.15 4731593.02
07:42:52         eth0 142781.00 3171600.00   9202.92 4689260.16
07:42:53         eth0 143835.00 3192932.00   9271.80 4720761.39
07:42:54         eth0 141922.00 3165174.00   9147.64 4679759.21
07:42:55         eth0 142993.00 3207038.00   9216.78 4741653.05
07:42:56         eth0 141394.06 3154335.64   9113.85 4663731.73
07:42:57         eth0 141850.00 3161202.00   9144.48 4673866.07
07:42:58         eth0 143439.00 3180736.00   9246.05 4702755.35
07:42:59         eth0 143501.00 3210992.00   9249.99 4747501.84
Average:         eth0 142835.66 3182165.93   9206.98 4704874.08
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>