nl80211: fix another nl80211_fam.attrbuf race

This is similar to the race Linus had reported, but in this case
it's an older bug: nl80211_prepare_wdev_dump() uses the wiphy
index in cb->args[0] as it is and thus parses the message over
and over again instead of just once because 0 is the first valid
wiphy index. Similar code in nl80211_testmode_dump() correctly
offsets the wiphy_index by 1, do that here as well.

Cc: stable@vger.kernel.org
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Git-commit: c319d50bfcf678c2857038276d9fab3c6646f3bf
Git-repo : git://git.kernel.org/pub/scm/linux/kernel/git/jberg/mac80211-next.git


Change-Id: I6590a6c28a81ac66d7fb6efc4690382a80bfddb4
CRs-fixed: 636257
Signed-off-by: Ahmad Kholaif <akholaif@codeaurora.org>