wireless: Set some stats used by /proc/net/wireless (wext)

Some stats for /proc/net/wireless (and wext in general) are not
being set.  This patch addresses a few of those with values easily
obtained from mac80211 core.

Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>