fxp entering promiscuous mode causing link to bounce

[YongHyeon PYUN]

On Fri, Mar 16, 2012 at 04:49:54PM -0400, Mike Tancsa wrote:
> I dont recall seeing this on RELENG_7, but I dont have a box to test with anymore confirm. On one box I upgraded to RELENG_8 I just noticed the nic will bounce if I enable tcpdump on it.  Sure enough, trying on a different RELENG_8 box with an fxp nic shows the same result.
> 
> eg
> 
> tcpdump -ni fxp0 -c 20
> 
> fxp0: link state changed to DOWN
> fxp0: promiscuous mode enabled
> fxp0: link state changed to UP
> fxp0: link state changed to DOWN
> fxp0: promiscuous mode disabled
> fxp0: link state changed to UP
> 
> I verified it on 2 different boxes. Is there a way to prevent this from happening ?
> 

It looks like a regression introduced in flow control support.
I think stable/7 also has the same code so you will see the same
issue on stable/7. However if you don't see the issue on stable/7 I
can't explain that.
Anyway, try attached patch and let me know how it works.  I found
other places which will result in link DOWN/UP so changed them to
get previous good behavior.
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