sfc: Stop masking out XGMII faults over reconfigures

The aim of this code was to avoid a spurious XGMII fault over a MAC
reconfigure. It's less relevant now that the PHY reconfigure isn't
called from the MAC reconfigure.

After applying this patch, our link stress test passed 48 hours of
testing without ever resetting the PHY.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>