ath fixes in -HEAD: squish (most) of the ath_rx_tasklet warnings

[Adrian Chadd]

Hi,

I've just rejiggled the reset/channel change path to (mostly) properly
drain and pause the ath taskqueue when doing a reset/channel change.

This has quietened most of the overlapping RX completions during reset
- they seemed to have been occuring because an RX interrupt was coming
in or had just come in before a reset.

Please test the latest -HEAD and let me know if there are any issues.

Thanks!


Adrian