mac80211: properly deal with station hashtable insert errors

mac80211: properly deal with station hashtable insert errors

BugLink: http://bugs.launchpad.net/bugs/1573034
commit 62b14b241ca6f790a17ccd9dd9f62ce1b006d406 upstream.

The original hand-implemented hash-table in mac80211 couldn't result
in insertion errors, and while converting to rhashtable I evidently
forgot to check the errors.

This surfaced now only because Ben is adding many identical keys and
that resulted in hidden insertion errors.

Fixes: 7bedd0cfad4e1 ("mac80211: use rhashtable for station table")
Reported-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>