virtio-net: fix a race on 32bit arches

virtio-net: fix a race on 32bit arches

commit 3fa2a1df909 (virtio-net: per cpu 64 bit stats (v2)) added a race
on 32bit arches.

We must use separate syncp for rx and tx path as they can be run at the
same time on different cpus. Thus one sequence increment can be lost and
readers spin forever.

Signed-off-by: Eric Dumazet <[email protected]>
Cc: Stephen Hemminger <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Cc: Jason Wang <[email protected]>
Acked-by: Rusty Russell <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: David S. Miller <[email protected]>