mac80211: fix hard lockup in sta_addba_resp_timer_expired

mac80211: fix hard lockup in sta_addba_resp_timer_expired

Problem is 2.6.35 specific, bug was introduced in backport
of upstream 44271488b91c9eecf249e075a1805dd887e222d2 commit.

We can not call del_timer_sync(addba_resp_timer) from
___ieee80211_stop_tx_ba_session(), as this function can be called from
that timer callback. To fix, simply use not synchronous del_timer().

Resolve https://bugzilla.redhat.com/show_bug.cgi?id=667459

Reported-and-tested-by: Mathieu Chouquet-Stringer <mathieu-acct@csetco.com>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>