typhoon: fix a race in typhoon_do_get_stats

Its important to store 'final' values in counters,
not using them as temporary variables,
or this might break some SNMP applications.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: David Dillow <dave@thedillows.org>
Signed-off-by: David S. Miller <davem@davemloft.net>