cfg80211: fix for duplicate userspace replies

cfg80211: fix for duplicate userspace replies

This fixes an incorrect assumption (BUG_ON) made in
cfg80211 when handling country IE regulatory requests.
The assumption was that we won't try to call_crda()
twice for the same event and therefore we will not
recieve two replies through nl80211 for the regulatory
request. As it turns out it is true we don't call_crda()
twice for the same event, however, kobject_uevent_env()
*might* send the udev event twice and/or userspace can
simply process the udev event twice. We remove the BUG_ON()
and simply ignore the duplicate request.

For details refer to this thread:

http://marc.info/?l=linux-wireless&m=124149987921337&w=2

Cc: stable@kernel.org
Reported-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>