mac80211: fix debugfs lockup

When debugfs_create_dir fails, sta_info_debugfs_add_work will not
terminate because it will find the same station again and again.
This is possible whenever debugfs fails for whatever reason; one
reason is a race condition in mac80211, unfortunately we cannot
do much about it, so just document it, it just means some station
may be missing from debugfs.

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

diff --cc net/mac80211/debugfs_sta.c
Simple merge

diff --cc net/mac80211/sta_info.c
Simple merge

diff --cc net/mac80211/sta_info.h
Simple merge