mac80211: correct aid location in peering frames

According to 802.11-2012 8.5.16.3.2 AID comes directly after the
capability bytes in mesh peering confirm frames.  The existing
code, however, was adding a 2 byte offset to this location,
resulting in garbage data going out over the air.  Remove the
offset to fix it.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>