wext: remove atomic requirement for wireless stats

The requirement for wireless stats to be atomic is now mostly
artificial since we hold the rtnl _and_ the dev_base_lock for
iterating the device list. Doing that is not required, just the
rtnl is sufficient (and the rtnl is required for other reasons
outlined in commit "wext: fix get_wireless_stats locking").

This will fix http://bugzilla.kernel.org/show_bug.cgi?id=13344


and make things easier for drivers.

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