r8169: add 64bit statistics.

Switch to use ndo_get_stats64 to get 64bit statistics.
Two sync entries are used (one for Rx and one for Tx).

Signed-off-by: Junchang Wang <junchangwang@gmail.com>
Reviewed-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>