rt2x00: disable TKIP on USB

On USB we can not get atomically TKIP key. We have to disable support
for TKIP acceleration on USB hardware to avoid bug as showed bellow.

[  860.827243] BUG: scheduling while atomic: hostapd/3397/0x00000002
<snip>
[  860.827280] Call Trace:
[  860.827282]  [<ffffffff81682ea6>] dump_stack+0x4d/0x66
[  860.827284]  [<ffffffff8167eb9b>] __schedule_bug+0x47/0x55
[  860.827285]  [<ffffffff81685bb3>] __schedule+0x733/0x7b0
[  860.827287]  [<ffffffff81685c59>] schedule+0x29/0x70
[  860.827289]  [<ffffffff81684f8a>] schedule_timeout+0x15a/0x2b0
[  860.827291]  [<ffffffff8105ac50>] ? ftrace_raw_event_tick_stop+0xc0/0xc0
[  860.827294]  [<ffffffff810c13c2>] ? __module_text_address+0x12/0x70
[  860.827296]  [<ffffffff81686823>] wait_for_completion_timeout+0xb3/0x140
[  860.827298]  [<ffffffff81080fc0>] ? wake_up_state+0x20/0x20
[  860.827301]  [<ffffffff814d5b3d>] usb_start_wait_urb+0x7d/0x150
[  860.827303]  [<ffffffff814d5cd5>] usb_control_msg+0xc5/0x110
[  860.827305]  [<ffffffffa02fb0c6>] rt2x00usb_vendor_request+0xc6/0x160  [rt2x00usb]
[  860.827307]  [<ffffffffa02fb215>] rt2x00usb_vendor_req_buff_lock+0x75/0x150 [rt2x00usb]
[  860.827309]  [<ffffffffa02fb393>] rt2x00usb_vendor_request_buff+0xa3/0xe0 [rt2x00usb]
[  860.827311]  [<ffffffffa023d1a3>] rt2x00usb_register_multiread+0x33/0x40 [rt2800usb]
[  860.827314]  [<ffffffffa05805f9>] rt2800_get_tkip_seq+0x39/0x50  [rt2800lib]
[  860.827321]  [<ffffffffa0480f88>] ieee80211_get_key+0x218/0x2a0  [mac80211]
[  860.827322]  [<ffffffff815cc68c>] ? __nlmsg_put+0x6c/0x80
[  860.827329]  [<ffffffffa051b02e>] nl80211_get_key+0x22e/0x360 [cfg80211]

Cc: stable@vger.kernel.org
Reported-and-tested-by: Peter Wu <lekensteyn@gmail.com>
Reported-and-tested-by: Pontus Fuchs <pontus.fuchs@gmail.com>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2x00mac.c

@@ -487,6 +487,8 @@ int rt2x00mac_set_key(struct ieee80211_hw *hw, enum set_key_cmd cmd,
 	crypto.cipher = rt2x00crypto_key_to_cipher(key);
 	if (crypto.cipher == CIPHER_NONE)
 		return -EOPNOTSUPP;
+	if (crypto.cipher == CIPHER_TKIP && rt2x00_is_usb(rt2x00dev))
+		return -EOPNOTSUPP;
 
 	crypto.cmd = cmd;