ath6kl: provide 64-bit per-station byte counters

Internally, 64-bit byte counters maintained for per-station
statistics. Tell to the netlink that full 64-bit value provided

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>