Trigerring a taskqueue from the if_start routine crashes FreeBSD6

[Sebastien]

> I don't see anything in output_layer.c   

output_layer was OK. I finally managed to track down this bug : it is not in 
the taskqueue system, but sending the incrimined frames enables the device to 
receive packets, and the bug was in the RX path. Its randomness was because 
the crash depended on wireless APs around...

> Note that it's ok to hold locks  
> over a call to free() so that your output_free() routine could be
> simplified somewhat:

Ok, applied. 

Thanks.

Sebastien