mac80211_hwsim: fix possible race condition in usage of info->control.sta & control.vif

info->control.sta and control.vif may only be dereferenced during the
drv_tx call otherwise could lead to use-after-free bugs.

Signed-off-by: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>