this driver by introducing a flag saying we already stopped the device.
On my Soekris net4801, this took a ping -i 0.001 from spending 80% of
time in interrupt handling to 10% (approx numbers).
This was a particular problem for the net4801 because the tree
interfaces share the same interrupt, but it would be a problem for
any configuration where an unused if_sis interface shares an interrupt
with a busy device.
Other drivers may have similar problems.
Thanks to: Luigi