mac80211: take statistics before encryption

When encryption is used, the number of bytes
sent to the peer increases by the IV and ICV.
This is accounted if software encryption is
used, but not if the devices does hardware
encryption. To make the numbers comparable,
never account for that overhead.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>