This fixes a non-theoretical race condition when transmitting and
receiving frames during a scan.  If the channel or operating band
changes while processing status descriptors in the tasklets, ath5k
will incorrectly use the new channel and band when reporting the
rates, even if the frame was actually sent on a previous channel.

Typically this will manifest as a beacon found on an incorrect
frequency and/or a warning in the driver while scanning:

[ 4773.891944] cfg80211: Found new beacon on frequency: 5805 MHz (Ch 161) on phy0
[ 4785.461125] ------------[ cut here ]------------
[ 4785.461135] WARNING: at drivers/net/wireless/ath/ath5k/base.c:1141 ath5k_tasklet_rx+0x2ff/0x577 [ath5k]()
[ 4785.461143] Hardware name: MacBook1,1
[ 4785.461148] invalid hw_rix: 1b
[ 4785.461152] Modules linked in: fuse i915 drm af_packet acpi_cpufreq binfmt_misc dm_mirror dm_region_hash dm_log dm_multipath dm_mod arc4 ecb snd_hda_codec_idt snd_hda_intel snd_hda_codec snd_seq_dummy snd_seq_oss snd_seq_midi_event ath5k snd_seq hid_apple usbhid snd_seq_device mac80211 appletouch snd_pcm_oss sky2 ohci1394 snd_mixer_oss ath ieee1394 snd_pcm bitrev snd_timer cfg80211 crc32 snd snd_page_alloc button processor ac ehci_hcd joydev uhci_hcd sg battery thermal sr_mod cdrom applesmc evdev input_polldev unix [last unloaded: microcode]
[ 4785.461296] Pid: 0, comm: swapper Tainted: G        W  2.6.30-rc3-wl #112
[ 4785.461302] Call Trace:
[ 4785.461316]  [<c012590f>] warn_slowpath+0x76/0xa5
[ 4785.461331]  [<c0219839>] ? debug_dma_unmap_page+0x5a/0x62
[ 4785.461357]  [<f9982f88>] ath5k_tasklet_rx+0x2ff/0x577 [ath5k]
[ 4785.461371]  [<c01446f7>] ? trace_hardirqs_off+0xb/0xd
[ 4785.461381]  [<c0129928>] ? __tasklet_schedule+0x6e/0x7c
[ 4785.461392]  [<c0129b02>] tasklet_action+0x92/0xe5
[ 4785.461402]  [<c0129f91>] __do_softirq+0xb1/0x182
[ 4785.461411]  [<c012a092>] do_softirq+0x30/0x48
[ 4785.461428]  [<c012a20a>] irq_exit+0x3d/0x74
[ 4785.461435]  [<c035a0de>] do_IRQ+0x76/0x8c
[ 4785.461440]  [<c010312e>] common_interrupt+0x2e/0x34
[ 4785.461445]  [<c014007b>] ? timer_list_show+0x1ab/0x939
[ 4785.461457]  [<f85fd25c>] ? acpi_idle_enter_bm+0x27c/0x2b9 [processor]
[ 4785.461463]  [<c02d1ed6>] cpuidle_idle_call+0x6a/0x9c
[ 4785.461468]  [<c0101cc8>] cpu_idle+0x53/0x87
[ 4785.461473]  [<c0346584>] rest_init+0x6c/0x6e
[ 4785.461479]  [<c04df74d>] start_kernel+0x286/0x28b
[ 4785.461484]  [<c04df037>] __init_begin+0x37/0x3c
[ 4785.461487] ---[ end trace aaf8496ba3679dfb ]---
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>