mac80211: remove association work when processing deauth request

In https://bugzilla.kernel.org/show_bug.cgi?id=15794

 a user encountered the
following:

[18967.469098] wlan0: authenticated
[18967.472527] wlan0: associate with 00:1c:10:b8:e3:ea (try 1)
[18967.472585] wlan0: deauthenticating from 00:1c:10:b8:e3:ea by local choice (reason=3)
[18967.672057] wlan0: associate with 00:1c:10:b8:e3:ea (try 2)
[18967.872357] wlan0: associate with 00:1c:10:b8:e3:ea (try 3)
[18968.072960] wlan0: association with 00:1c:10:b8:e3:ea timed out
[18968.076890] ------------[ cut here ]------------
[18968.076898] WARNING: at net/wireless/mlme.c:341 cfg80211_send_assoc_timeout+0xa8/0x140()
[18968.076900] Hardware name: GX628
[18968.076924] Pid: 1408, comm: phy0 Not tainted 2.6.34-rc4-00082-g250541f-dirty #3
[18968.076926] Call Trace:
[18968.076931]  [<ffffffff8103459e>] ?  warn_slowpath_common+0x6e/0xb0
[18968.076934]  [<ffffffff8157c2d8>] ?  cfg80211_send_assoc_timeout+0xa8/0x140
[18968.076937]  [<ffffffff8103ff8b>] ? mod_timer+0x10b/0x180
[18968.076940]  [<ffffffff8158f0fc>] ?  ieee80211_assoc_done+0xbc/0xc0
[18968.076943]  [<ffffffff81590d53>] ?  ieee80211_work_work+0x553/0x11c0
[18968.076945]  [<ffffffff8102d931>] ? finish_task_switch+0x41/0xb0
[18968.076948]  [<ffffffff81590800>] ?  ieee80211_work_work+0x0/0x11c0
[18968.076951]  [<ffffffff810476fb>] ? worker_thread+0x13b/0x210
[18968.076954]  [<ffffffff8104b6b0>] ?  autoremove_wake_function+0x0/0x30
[18968.076956]  [<ffffffff810475c0>] ? worker_thread+0x0/0x210
[18968.076959]  [<ffffffff8104b21e>] ? kthread+0x8e/0xa0
[18968.076962]  [<ffffffff810031f4>] ?  kernel_thread_helper+0x4/0x10
[18968.076964]  [<ffffffff8104b190>] ? kthread+0x0/0xa0
[18968.076966]  [<ffffffff810031f0>] ?  kernel_thread_helper+0x0/0x10
[18968.076968] ---[ end trace 8aa6265f4b1adfe0 ]---

As explained by Johannes Berg <johannes@sipsolutions.net>:

We authenticate successfully, and then userspace requests association.
Then we start that process, but the AP doesn't respond. While we're
still waiting for an AP response, userspace asks for a deauth. We do
the deauth, but don't abort the association work. Then once the
association work times out we tell cfg80211, but it no longer wants
to know since for all it is concerned we accepted the deauth that
also kills the association attempt.

Fix this by, upon receipt of deauth request, removing the association work
and continuing to send the deauth.

Unfortunately the user reporting the issue is not able to reproduce this
problem anymore and cannot verify this fix. This seems like a well understood
issue though and I thus present the patch.

Bug-identified-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>