Use 64-bit TX/RX byte counters for statistics

Use 64-bit TX/RX byte counters for statistics

If the driver supports 64-bit TX/RX byte counters, use them directly.
The old 32-bit counter extension is maintained for backwards
compatibility with older drivers.

For nl80211 driver interface, the newer NL80211_STA_INFO_RX_BYTES64 and
NL80211_STA_INFO_TX_BYTES64 attributes are used when available. This
resolves the race vulnerable 32-bit value wrap/overflow. Rework RADIUS
accounting to use these for Acct-Input-Octets, Acct-Input-Gigawords,
Acct-Output-Octets, and Acct-Output-Gigawords, these values are often
used for billing purposes.

Signed-off-by: Nick Lowe <nick.lowe@lugatech.com>