On some laptops, under very high loads, the socket event register read

On some laptops, under very high loads, the socket event register read
in the ISR doesn't read the actual socket event register, but instead
reads garbage (usually 0xffffffff, but other times other things).
This totally violates the PCI spec, but happens rarely enough that a
workaround is in order.  This adds one test when we have a real
interrupt to service (which is very rare), and doesn't affect the
usualy 'nothing to see here' case at all.

Problem reported by many, but sam@ gave me this workaround after
diagnosing the problem.