The rewrite of the interrupt handler includes:
o loop until all pending interrupts are handled. This closes a
race condition.
o count the number of interrupt sources we handled so that we can
properly return FILTER_HANDLED or FILTER_STRAY when we break out
of the loop.
o When matching the interrupt source to the devices that have that
source pending, check only from the set of devices we found to
have a pending interrupt.
PR: kern/140947
MFC after: 3 days
57467e5933