bna: fix stats handling

get_stats() method incorrectly clears a global array before folding
various stats. This can break SNMP applications.

Switch to 64 bit flavor to work on a user supplied buffer, and provide
64bit counters even on 32bit arches.

Fix a bug in bnad_netdev_hwstats_fill(), for rx_fifo_errors, missing a
folding (only the last counter was taken into account)

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