b43: Mask PHY TX error interrupt, if not debugging

b43: Mask PHY TX error interrupt, if not debugging

This masks the PHY TX error interrupt, if debugging is disabled.

Currently we have a bug somewhere which triggers this interrupt once
in a while. (Depends on the network noise/quality). While this is nonfatal,
it scares the hell out of users and we frequently receive bugreports
that incorrectly identify this error message as the reason.

There's another problem with this. The PHY TX error interrupt is protected
with a watchdog that will restart the device if it keeps triggering very often.
This is used to fix interrupt storms from completely broken devices.

However, this watchdog might trigger in completely normal operation.
If the TX capacity of the card is saturated, the likeliness of the watchdog
triggering increases, as more TX errors occur. The current threshold
for the watchdog is 1000 errors in 15 seconds.

This patch adds a workaround for the issue by just enabling the interrupt
if debugging is disabled (by Kconfig or by modparam).

This has the downside that real fatal PHY TX errors are not caught anymore.
But this is nonfatal due to the following reasons:
* If the card is not able to transmit anymore, MLME will notice anyway.
* I did _never_ see a real fatal PHY TX error in a mainline b43 driver.
* It does _not_ result in interrupt storms or something like that.
  It will simply result in a stalled card. It can be debugged by enabling
  the debugging module parameter.

Signed-off-by: Michael Buesch <mb@bu3sch>
Signed-off-by: John W. Linville <linville@tuxdriver.com>