intel.lua: Fixed for bug with 64-bit descriptor addresses.

Great detective work by @pkazmier to find the bug an @rahul-mr to
confirm the fix. This seems to make HugeTLB support work reliably.
Descriptor ring addresses were being truncated to 32 bits and this
would break DMA whenever the memory was allocated in high addresses,
tending to happen on physical machines with >4GB RAM more than VMs.

Cool!

See discussion of commit f5a3431ab266786f663c6e1d006c12765c25970b.

Closes issue #39.