tg3: 64 bit stats on all arches

Now core network is able to handle 64 bit netdevice stats on 32 bit
arches, we can provide them for tg3, since hardware maintains 64 bit
counters.

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